Sum of reciprocals of all positive integers which do not contain the digit $9$
18064
Sum of reciprocals of numbers with certain terms omitted
75166
Find with proof all positive integers $n$ such that $2^n + 1 \equiv 0 \pmod{n}$
15599
Given that a,b,c are distinct positive real numbers, prove that (a + b +c)( 1/a + 1/b + 1/c)>9
31184
Sums of powers below a prime
94871
Sum of an unorthodox infinite series
117380
Divisibility Rule for 9
34784
Is a number meeting these conditions divisible by forty-nine?
64592
The last two digits of $9^{9^9}$
35515
Find the number of $(m+n)$ digit binary sequences with $m$ $0$'s and $n$ $1$'s such that no two $1$'s are adjacent
153302
$9$ divides $n-r(n)$ where $r(n)$ is $n$ with its digits reversed
77200
Prove:that in any set of 1009 positive integers exits two numbers $a_i$ and $a_j$ such that $a_i-a_j$ or $a_i+a_j$ is divisible by 2014
45788
$n$-th digit in the sequence of natural numbers
71789
Prove that the sum of digits of $(999...9)^{3}$ (cube of integer with $n$ digits $9$) is $18n$
79718
Does the alternating sum of prime reciprocals converge?
113695
Show that there is no integer n with $\phi(n)$ = 14
68903
The number $2^{29}$ has exactly $9$ distinct digits. Which digit is missing?
41002
sum of integers using order of integers and primitive roots