Curiosity about a simple identity Consider the well known formula
$$1^3 + 2^3 +\cdots+ n^3 = (1+\cdots+n)^2  , n \in N$$
Now suppose that for all $n \in N$ the identity is true :
$$1^k + 2^k +\cdots+ n^k = (1+\cdots+n)^{k-1}  $$
with $k \in N$ fixed. Which is the possible values of $k$ ?
Someone could point me a reference?
Sorry for my english, it is not good
Thanks in advance

Consider the case when $n = 2$. Then we have that $1 + 2^k = 3^{k-1}$. By Catalan's Conjecture (Mihăilescu's theorem), we have that $k = 3$ (the theorem basically states that the only two consecutive perfect powers are $2^3$ and $3^2$.)
