OFFSET
1,3
EXAMPLE
a(5) = 17; a(5) = Sum_{i=1..2} sigma_k(5-k) = sigma_1(4) + sigma_2(3) = (1+2+4) + (1^2+3^2) = 7 + 10 = 17.
MATHEMATICA
Table[Sum[DivisorSigma[i, n - i], {i, Floor[n/2]}], {n, 30}]
PROG
(PARI) a(n) = sum(k=1, n\2, sigma(n-k, k)); \\ Michel Marcus, Apr 29 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Apr 29 2021
STATUS
approved