4 About The Sum of Positive Divisors of $n$ 4 What number comes next in this sequence? 3 Linear Diophantine equation which doesn't divide 2 What's $1^3+2^3+3^3+\cdots+99^3$ modulo $3$? 2 $17 | 29x + 18y \implies 17 | 23x + 9y$

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### Questions (30)

 4 A Proposition related to Fermat Factorization Method 3 About The Sum of Positive Divisors of $n$ 3 Factor $10^6-1$ completely 2 Is the equation $x = \phi(n), x=2k, n,k \in \mathbb{Z}$, where $\phi(n)$ is the Euler totient function, solvable for all evens? 2 Find all Pythagorean triples $x^2+y^2=z^2$ where $x=21$

### Tags (52)

 15 elementary-number-theory × 55 4 multiplicative-function × 4 11 divisibility × 32 4 divisor-sum × 2 7 number-theory × 33 4 arithmetic-functions × 2 7 prime-numbers × 8 4 pattern-recognition 4 modular-arithmetic × 22 4 sequences-and-series

### Bookmarks (42)

 401 How can I evaluate $\sum_{n=0}^\infty(n+1)x^n$? 152 How to prove: if $a,b \in \mathbb N$, then $a^{1/b}$ is an integer or an irrational number? 108 How do I compute $a^b\,\bmod c$ by hand? 100 What is the Jacobian matrix? 88 Divisibility by 7 rule, and Congruence Arithmetic Laws