Leroy Quet wrote:
> Let sigma(k) = sum{j|k} j.
> Let phi(k) be the number of positive integers <= k and coprime to k.
>
> Then for which n's is
>
> product{k=1 to n} sigma(k)/phi(k)
>
> an integer?
I've got
1 2 3 4 6 7 8 14 15
and no other n up to 10000.
Max