OFFSET
1,3
COMMENTS
If p is prime, a(p) = Sum_{d|p} (p-d)^sigma(p/d) = (p-1)^(p+1).
EXAMPLE
a(10) = Sum_{d|10} (10-d)^sigma(10/d) = 9^18 + 8^6 + 5^3 + 0^1 = 150094635297261390.
MATHEMATICA
Table[Sum[(n - k)^DivisorSigma[1, n/k] (1 - Ceiling[n/k] + Floor[n/k]), {k, n}], {n, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Jun 12 2021
STATUS
approved