Mathematics
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Ivan Loh
  • Member for 9 years, 4 months
  • Last seen more than 7 years ago
  • Singapore
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286 Answers

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57 votes

A question comparing $\pi^e$ to $e^\pi$

45 votes
Accepted

Math Olympiad Prime Number Question

42 votes
Accepted

Pattern to last three digits of power of $3$?

28 votes
Accepted

Limit of $y=\sqrt{5+\sqrt{5-\sqrt{5+\sqrt{5-\sqrt{5+\ldots}}}}}$

28 votes
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Show that $4mn-m-n$ can never be a square

21 votes
Accepted

Finite Sum $\sum\limits_{k=1}^{m-1}\frac{1}{\sin^2\frac{k\pi}{m}}$

19 votes

Find the minimum value of $|\sin x+\cos x+\tan x+\cot x+\sec x+\csc x|$ for real numbers $x$

17 votes
Accepted

Prove $\frac{a}{ab+2c}+\frac{b}{bc+2a}+\frac{c}{ca+2b} \ge \frac 98$

17 votes
Accepted

Problems regarding $\{x_n \}$ defined by $x_1=1$; $x_n$ is the smallest distinct natural number such that $x_1+...+x_n$ is divisible by $n$.

16 votes
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Let $p$ be an odd prime number. How many $p$-element subsets of $\{1,2,3,4, \ldots, 2p\}$ have sums divisible by $p$?

16 votes
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To prove that $2^{3n}+2^n +1$ is not a perfect square.

16 votes
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Is there a $3\times 3$ magic square adding up to $7$?

14 votes
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Placing numbers around a circle

12 votes
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Solve $3^x + 28^x=8^x+27^x$

12 votes
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How many different game situations has connect four?

12 votes
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Find all functions that satisfy $f(f(x)+y)=2x+f(f(y)-x)$

12 votes
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Do there exist infinitely many pairs of primes $(p,q)$ such that $pq$ divides $2^{p-1}+2^{q-1}-2$?

12 votes
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Solve in the positive real number the system of equation.

12 votes
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How many integers between [3,000, 8,000] have digit sum 20?

11 votes
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Proving that a number with digits 1...9 in some order, ending in 5, is not a perfect square.

11 votes
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sum of the product of consecutive legendre symbols is -1

11 votes
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Find all natural numbers such that $\sum_{k=1}^{n} \frac{n^k}{k!}$ is an integer

10 votes

Congruences and prime powers

10 votes
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How to find $1+\dfrac{1}{a_{1}}+\dfrac{1}{a_{2}}+\cdots+\dfrac{1}{a_{n}}$

10 votes
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What is the last non-zero digit of $50!$?

10 votes
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Sets $f_n\in A_f$ where $f_{n+1}=f_n \circ S \circ f^{\circ (-1)}_n$ and operator $\alpha(f_n)=f_{n+1}$

9 votes

Find all solutions: $x^2 + 2y^2 = z^2$

9 votes
Accepted

$5 \frac {3}{*} \times 3 \frac {*}{2}=19$?

9 votes
Accepted

Bounds on a sum of gcd's

9 votes
Accepted

How can prove this equation.

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