Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #12 May 19 2021 11:41:11
%S 0,1,3,9,17,55,111,457,943,4962,11148,69526,159402,1161340,2765874,
%T 22829766,55192956,510771772,1257880780,12870681814,32042113008,
%U 359566186586,904795505226,11043196798176,28002785395660,369463867367567,943392140873807,13378621275148931
%N a(n) = Sum_{k=1..floor(n/2)} sigma_k(n-k), where sigma_k(n) is the sum of the k-th powers of the divisors of n.
%e 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.
%t Table[Sum[DivisorSigma[i, n - i], {i, Floor[n/2]}], {n, 30}]
%o (PARI) a(n) = sum(k=1, n\2, sigma(n-k, k)); \\ _Michel Marcus_, Apr 29 2021
%Y Cf. A245466.
%K nonn
%O 1,3
%A _Wesley Ivan Hurt_, Apr 29 2021