1
vote
2answers
44 views

Conjecture: When does $n=ab$, with $a\leq b\leq 2a$?

I conjecture that if this occurs, $a$ and $b$ are unique. Obviously if $n$ is an odd prime, this does not occur, and if $n=a^2$, it does. In any case, what is the set of numbers such that this sort of ...
0
votes
1answer
135 views

For all $n$, $9^n + 25^n - 1$ has a prime factor with $7$ in its decimal representation?

Let $x_n$ be a sequence of positive integers defined by $x_n=9^n + 25^n -1$ for all $n \ge 2$ I conjectured that there exists at least one prime divisor of $x_n$ which contains $7 $ in its decimal ...
0
votes
1answer
48 views

Conjecture linking multiplicative order of $2$ and semi-primes

Suppose we have a semi-prime $N=pq$, where $p \ne q$, and $p>2$, $q>2$ Let $k$ be the multiplicative order of $2$ mod $N$, then either $p^{2} \bmod k \equiv 1$ or $q^{2} \bmod k \equiv 1$ Is ...
4
votes
2answers
122 views

Conjecture involving semi-prime numbers of the form $2^{x}-1$

Let $x$ be a positive integer such that $(2^{x}-1)=pq$ , where $p$ and $q$ are prime numbers. I want to show that either $p^{2} \bmod x \equiv 1$ or $q^{2} \bmod x \equiv 1$ (or both of course). Is ...
2
votes
2answers
152 views

Number of subsets of $U$ whose arithmetic mean is integral

Question is :- $n$ is a positive integer. Call a non-empty subset $S$ of $\{1,2,\dots,n\}$ "good" if the arithmetic mean of elements of $S$ is also an integer. Further Let $t_n$ denote the ...
2
votes
3answers
283 views

Is this statement stronger than the Collatz conjecture?

$n$,$k$, $m$, $u$ $\in$ $\Bbb N$; Let's see the following sequence: $x_0=n$; $x_m=3x_{m-1}+1$. I am afraid I am a complete noob, but I cannot (dis)prove that the following implies the ...
1
vote
1answer
773 views

Why proof by induction fails for Goldbach's conjecture?

Can anyone clarify why induction method fails for this conjecture?
1
vote
2answers
355 views

twin prime conjecture

Whether I am correct or wrong I don't know. If there are any corrections, please let me know. Let $p_n$ = product of all primes. (of course we can go still beyond as we know $p_n$ is infinite). Now ...
3
votes
2answers
404 views

A conjecture about the form of some prime numbers

Let $k$ be an odd number of the form $k=2p+1$ ,where $p$ denote any prime number, then it is true that for each number $k$ at least one of $6k-1$, $6k+1$ gives a prime number. Can someone prove or ...