Sums of squares (Proof)
134834
$n^2 + (n+1)^2 = m^3$ has no solution in the positive integers
63879
Prove that $\sum_{k=0}^r {m \choose k} {n \choose r-k} = {m+n \choose r}$
88759
Proofs of Sylow theorems
92784
Intuitive (combinatorial) proof of $2^n=\sum_{k=0}^n {n\choose k}$
4194
Which integers can be expressed as a sum of squares of two coprime integers?
5049
Proving $\sum_{k=0}^n(-1)^k\binom nk=0$
84010
Combinatorial proof that $\sum \limits_{k=0}^n \binom{2k}{k} \binom{2n-2k}{n-k} (-1)^k = 2^n \binom{n}{n/2}$ when $n$ is even
20443
Calculate sum of squares of first $n$ odd numbers
57986
Sum of products of combinatorials
62747
Use induction to prove a product of sums of squares is a sum of squares
26790
Proving the geometric sum formula by induction
120976
Proving $\sum_{k=0}^{n}k{n\choose k}^2 = n{2n-1 \choose n-1} $
108596
Proof by induction for "sum-of"
98440
Show that any non-negative rational integer may be written as the sum of two squares if it is of the form....
7073
How to get to the formula for the sum of squares of first n numbers?
101899
Proof By Induction of a Sum
92704
Prove that $\sum_{k=1}^{n}k\binom{n}{k}=n\cdot2^{n-1}$