OFFSET
1,1
COMMENTS
It is easy to see that {sigma_k(N) mod N: k >= A051903(N)} is purely periodic.
All terms are nonsquarefree: if N is squarefree and N is here, then A328919(N) < A051903(N) = 1, so A328919(N) = 0. By the property mentioned in A328919, a necessary condition is that for every prime p dividing N, write N = p*s, we have p divides d(s), d = A000005. But d(s) is a power of 2, so N = 2, and 2 is not here.
EXAMPLE
CROSSREFS
KEYWORD
nonn
AUTHOR
Jianing Song, Oct 31 2019
STATUS
approved