Prime numbers are natural numbers greater than 1 not divisible by any smaller number other than 1. This tag is intended for questions about, related to, or involving prime numbers.

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prime powers modulo prime

I stumbled upon the following property: $n\equiv n^5\bmod 5$ for all $n\in\mathbb{Z}$, so out of I tried other (prime) numbers $n\equiv n^p\bmod p$. My question is whether this is true for all primes ...
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Prime Mean of Primes

1) Are there infinitely many primes $p_1,p_2$ such that $\frac{p_1+p_2}{2}$ is also prime? 2) What can we say about the more general problem : Are there infinitely many primes $p_1,p_2,\cdots, p_n$...
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Is this a recurrence for the characteristic sequence of composite numbers?

The characteristic sequence of composite numbers is equal to 1 if $n$ is not a prime number and equal to 0 if $n$ is a prime number, starting: $$1, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1,...$$ where the ...
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totally split primes in a number field

I have to show: For any number field $K$, there are infinitely many prime numbers $p \in \mathbb{N}$, that are totally split in $K$. I think have already shown (with some hints my professor gave) ...
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Application of prime number theorem

In the following I am referring to a small argument made in "A counterexample to Borsuk's conjecture" by Jeff Kahn, Gil Kalai (see http://arxiv.org/abs/math.MG/9307229) In this paper the authors bound ...
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Prime Number Theorem and sum of reciprocals of primes

This is not a homework problem. I am a mathematician (group representations and classical analysis) who never studied number theory and am beginning with Niven’s book. My question concerns the ...
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Finding a prime number between $n$ and $2n$

I am trying to find a prime number between $n$ and $2n$. I know that the number of primes between $n$ and $2n$ is $n/(2\ln n)$. I was thinking of choosing a random number between $n$ and $2n$ and ...
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Number of primes less then $6000$ using $n/ \log n$

So I am trying to use this formula here and is giving me some trouble. If I just substitute $6000$ into the formula, the answer is approximately $1500$. But the number of primes under $6000$ is ...
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The prime number theorem and the nth prime

This is a much clearer restatement of an earlier question. In section 1.8 of Hardy & Wright, An Introduction to the Theory of Numbers, it is proved that the function inverse to $ x ⁄ \log⁡ x$ is ...
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An Inequality Involving Prime Numbers

Let $p_i$ be the $i^{th}$ prime number. It seems as though the following inequality is true for all positive integers $m$ and real numbers $x>1$: $$1+\frac{1}{p_m^x}\leq\prod_{i=m+1}^{\infty}\left(...
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Question regardles primes and the fundamental theorem of arithmetic

I have been reading through my book of practice proofs and came across this particular question which has stumped me. $p$ and $q$ are primes. Prove $\forall p \in \mathbb{Z}, \forall k \in \...
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Resources about infinite primes of form $n^2 + 1$

Where can one find existing work on the following problem? Prove there are infinitely many primes of the form $n^2 + 1$. Resources about related work would also be appreciated.
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Generalizing Ramanujan's proof of Bertrand's Postulate: Can Ramanujan's approach be used to show a prime between $4x$ and $5x$ for $x \ge 3$

Perhaps, I've been thinking too long about Ramanujan's proof, but it appears to me that his argument can be generalized beyond $x$ and $2x$. My argument below attempts to show that for $x \ge 1331$, ...
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Checking the Harald Helfgott proof of the little Goldbach conjecture without a public release of numerical checks?

A few month ago, a proof of the little/ternary Goldbach conjecture has been claimed by Harald Helfgott with three articles: Major arcs for Goldbach's theorem Minor arcs for Goldbach's theorem ...
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Ulam spiral: Is there an “unusual amount of clumping” in prime-rich quadratic polynomials?

I was reading Martin Gardner's Mathematical Games column on the Ulam spiral which appeared in the March 1964 issue of Scientific American. (The spiral actually featured on the cover of that issue.) ...
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Questions about central polygonal numbers $1, 2, 4, 7, 11, 16, 22, 29, 37, 46,\cdots$

Formula for Central polygonal numbers is $\frac{n(n+1)}{2} + 1$, if $n=1$ or $n$ is prime, we get the new sequence $A$: 2, 4, 7, 16, 29, 67, 92, 154, 191, ... It seems that all primes either is ...
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Birthday problem & primes

Let $\pi_k(n)$ be the almost prime counting function, then $\pi_k(2^kn)$ reaches a max value, since $\pi_k(2^kn)=\pi_{k+1}(2^{k+1}n)$ for large enough $k$. (eg, $\pi_{5}(272)=\pi_{6}(2\times272)=\...
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Equivalence to the prime number theorem

I was just reading this question and answer: How will this equation imply PNT and it raised a whole new question: Given that $\sum_{n\le x} \Lambda(n)=x+o(x)$, prove that $$\sum_{n\le x} \frac{...
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Can a Mersenne number be a power (with exponent > 1) of a prime?

Let $n \geq 1$ and consider the (Mersenne) number $M_n = 2^n-1$. Is it possible that $M_n = p^k$ for some prime $p$ and some (necessarily odd) $k > 1$? Thanks in advance.
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AP term multiple of prime number

I am having this equation : (a+(n-1)d)%p=0 Here a and d can go upto 10^18 and p is prime number upto 10^9 . How to find the least value of n here? Example : If ...
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Prime Triangle:: How to find the position(row and column) of prime number in a triangular arrangement

I was working on problem which asks the position of a prime number in a triangular arrangement. If we arrange the all prime up to 10^8 as shown in image we can find the row and column number of a ...
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Improving Bertrand's postulate

Recall that Bertrand's postulate states that for $n \ge 2$ there always exists a prime between $n$ and $2n$. Bertrand's postulate was proved by Chebyshev. Recall also that the harmonic series $$ 1 + \...
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How to combine three integers from three sequences such that all the numbers in the triplet be coprime.

So there are three sequences of integers denoted $s_1, s_2$ and $s_3$. Each of them starts at $2$ and goes up to an integer $N$. In other words, they're all identical sequences of numbers of the form $...
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Wolstenholme Number

Does Wolstenholme Numbers have perfect squares other than 1 and 49? The first few are 1, 5, 49, 205, 5269, 5369, 266681, 1077749 seems to be a complicated problem
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Extrema of the Ratio of Consecutive Primes

Let $p_i$ denote the $i$th prime number. We know that $\frac{p_{n+1}}{p_n}\rightarrow 1$ as $n\rightarrow\infty$. Therefore, if we pick some real number $c>1$, there should be some positive integer ...
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Physical reflections of prime-number distribution

Not a purely mathematical question: I have read somewhere that Atomic Orbital is closely related to the distribution of prime numbers, but I am unable to find any reference to that. Can someone ...
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277 views

Proof for Carmichael theorem

if $n=p_1^{a_1}p_2^{a_2}p_3^{a_3}\dots p_r^{a_r}$ and $\lambda(n) = lcm[(p_1-1)(p_1^{a_1-1}),(p_2-1)(p_2^{a_2-1}),(p_3-1)(p_3^{a_3-1}),\dots,(p_r-1)(p_r^{a_r-1})]$ then $k^{\lambda{n}} \equiv 1(...
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The binomial coefficients $\binom{n}{ p}$ are divisible by a prime $p$ only if $n$ is a power of $p.$

I'm looking for a "high school / undergraduate" demonstration for the: All the binomial coefficients $\binom{n}{i}=\frac{n!}{i!\cdot (n-i)!}$ for all i, $0\lt i \lt n$, are divisible by a prime $p$ ...
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How many $\overline{a}\in\left(\mathbb{Z}/91\mathbb{Z}\right)^\times$ pass the Fermat and Miller-Rabin primability tests?

Let $$\text{F}_{91}:=\left\{\overline{a}\in\left(\mathbb{Z}/n\mathbb{Z}\right)^\times:91\text { passes the Fermat primality test to base }a\right\}$$ and $$\text{MF}_{91}:=\left\{\overline{a}\in\left(\...
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A congruence involving prime numbers

This congruence appears in a textbook I'm reading anf it left the proof to the reader, however I cannot find my way around it. $$(a+b)^ p \equiv a^p+b^p \pmod p\text{ when $p$ prime and }a,b\in\...
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How can I solve this problem without having to do it by hand?

I'm dealing with the following problem in computational programming. I'm trying to find a way to build an algorithm that can quickly resolve the following problem statement without forcing me to do it ...
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Sum of odd prime and odd semiprime as sum of two odd primes?

How to prove that each sum of odd prime and odd semiprime can be written as sum of two odd primes $(p_1+p_2p_3=p_4+p_5)$ ? Since we know that each prime number greater than $3$ is of the form $6k\pm ...
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Twin primes : prove the convergence of $ \lim_{N\sim\infty} \frac{1}{N} \sum^{N}_{p\in T} (\log(p)+\frac{1}{p})²$

let $T$ be the twin primes set : $p \in T $ if and only if $ p$ and $p+2$ are primes. Can you help me establish the convergence of : $$ \lim_{N\sim\infty} \frac{1}{N} \sum^{N}_{p\in T} (\log(p)+\frac{...
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Combining primes for getting primes?

I was thinking about what would happen when we combine two prime numbers $p$ and $q$ into one number $:pq:$ . Like if $p=5$ and $q=3$ , then $:pq:=53$ . Then if $p=7$ and $q= 11$ then $:pq:=711$ and ...
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(p-1)! number theory problem

I was working on this little problem: Let $\frac{a}{(p-1)!} = 1 + 1/2 + 1/3 + ... + 1/(p-1)$, where p is a positive prime. (a) Prove $p\mid a$. (b) Can $p^2 \mid a$? I thought (a) was pretty self-...
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Is every prime the average of two other primes?

$\forall {p_1\in\mathbb{P}, p_1>3},\ \exists {p_2\in\mathbb{P},\ p_3\in\mathbb{P}};\ (p_1 \neq p_2) \land (p_1\neq p_3) \land (p_1 = \frac{p_2+p_3}{2})$ Now I'm not a 100% sure about this, but I ...
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Proof of infinitely many primes, clarification

Proof: The proof is by contradiction. Suppose there are only finitely many primes. Let the complete list be $p_1,p_2,\dots,p_n$. Let $N = p_1p_2 \dots p_n+1$. According to the Fundamental Theorem of ...
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Is $83^{27} +1 $ a prime number?

I'm having problems with exercises on proving whether or not a given number is prime. Is $83^{27} + 1$ prime?
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Why all composite numbers have this property?

Define $f(n)=\sum\limits_{A \in S} f_{1}(n,A),\ n>2,\ n \in \mathbb{Z}$, where $S$ is the power set of $\{\frac{1}{2},\cdots ,\frac{1}{n-1}\}$. Define $\ f_1(n,\varnothing)=1,\ f_{1}(n,A)=(-1)^{\...
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Beginner Proof about Primes

I am interested in understand the proof of infinitely many primes. It seems like quite an easy proof, ( I know there are many but I am referring to the proof that goes as follows); " Suppose there ...
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Infinite sum of prime reciprocals

Let $\mathbb D$ be the set of all real numbers that can be expressed as a sum of distinct prime reciprocals, i.e. $\mathbb D = \{ d \in \mathbb R \mid d = \sum_{k \in \mathbb K} \frac 1k $ for some (...
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Primes in a concave sequence

Are there infinitely many consecutive tuples of primes $(p_{n-1},p_n,p_{n+1})$ satisfying $$\frac{1}{2}(p_{n-1}+p_{n+1})\le p_n$$ I don't know how to do this problem. Maybe we use the prime number ...
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How can I solve this problem without doing it by hand? [duplicate]

I'm dealing with the following problem in computational programming. I'm trying to find a way to build an algorithm that can quickly resolve the following problem statement without forcing me to do it ...
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106 views

Is there any way to solve this problem without having to do it by hand? [duplicate]

I'm dealing with the following problem in computational programming. I'm trying to find a way to build an algorithm that can quickly resolve the following problem statement. Is there any way to group ...
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$\log$ approximation for $\pi(x)$

It seems that a reasonable $\log$ approximation for $\pi(x)$ can be given, where $f(y, x) := \log\left(\dfrac{\log(x)}{\log\left(e(y - \lfloor y\rfloor) + x^{1/x}(1 - y + \lfloor y\rfloor)\right)}\...
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Finding Prime triples with $p_{n} +p_{n+1} −p_{n+2} = 1$

I was just looking at a sequence of primes and suddenly I got this thought that $p_2 +p_3 −p_4 = 1$ since $p_2 = 3, p_3 = 5, p_4 = 7$. Also for $p_3 = 5, p_4 = 7, p_5 = 11$ one has $p_3 +p_4 −p_5 = 1$....
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Intuitively, what separates Mersenne primes from Fermat primes?

A Mersenne prime is a prime of the form $2^n-1$. A Fermat prime is a prime of the form $2^n+1$. Despite the two being superficially very similar, it is conjectured that there are infinitely many ...
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On non-divising primes of an integer $x$

We know more about divisor than non-divisors, If we consider the sets : $$P^{1}_{x} =\left \{ p \leq x : \ p \in \mathbb{P} \right \}$$ ($\mathbb{P} $ is the primes set) $$ P^{2}_{x} =\left \{ p_{i}...
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Relative error in prime number fitting

I got curious about what it would look like if I made a scatter plot of the n-th prime number as a function of n (lets call it p(n), so that p(1)=2, for instance ). Not being an expert in the area I ...
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How many natural value of n such that $n^5+2n^4+n-1$ is prime number?

From above polynomial, I can only get one value to make it prime. The value, I guess, is only one. For $n=1$, we got: $$(n^5+2n^4+n-1)= 1+2+1-1= 3 \quad\text{(prime)}$$ But, I cannot find the ...