How many natural numbers are multiples of both a and b?
1712
$ d_1,d_2\mid n\iff {\rm lcm}(d_1,d_2)\mid n\ $ [LCM Universal Property]
120744
How many $n\times m$ binary matrices are there, up to row and column permutations?
121918
Why is $5^{n+1}+2\cdot 3^n+1$ a multiple of $8$ for every natural number $n$?
126124
Why is the sum of the digits in a multiple of 9 also a multiple of 9?
45392
Every natural number can be written as the sum of distinct Fibonacci numbers?
6488
Proof that $n^3 + 3n^2 + 2n$ is a multiple of $3$.
115145
Show that $n-m$ is a multiple of 9 when $n$ and $m$ have same digits
150652
Number of 4-digit numerals with at most 2 different digits
78407
Are there infinitely-many numbers that are both square and triangular?
5375
Is there a bijective function mapping Natural numbers to Natural numbers, other than $f(n) = n$?
110958
How to solve for any given natural number n?
124890
Divisibility within a block of natural numbers
144025
Number of Solutions in this Number Puzzle
157212
Definition of Multiple .
48051
Proof related to natural numbers
149939
Number of ordered pairs $(a,b)$ such that $ab \le 3600$
45788
$n$-th digit in the sequence of natural numbers