OFFSET
1,3
FORMULA
a(n) = Sum_{i=1..floor(n/2)} sigma(i*(n-i)).
EXAMPLE
a(5) = 19; the partitions of 5 into two parts are (1,4) and (2,3). The sum of divisors of the products of the partitions is sigma(4) + sigma(6) = (1+2+4) + (1+2+3+6) = 7 + 12 = 19.
MATHEMATICA
Table[Sum[DivisorSigma[1, i*(n - i)], {i, Floor[n/2]}], {n, 80}]
PROG
(PARI) a(n) = sum(i=1, n\2, sigma(i*(n-i))); \\ Michel Marcus, Mar 18 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Mar 18 2016
STATUS
approved