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 #10 Aug 16 2019 07:52:55
%S 1,4,10,27,73,227,767,2860,11569,50363,234155,1156037,6031747,
%T 33130183,190929773,1151198266,7243777228,47462906925,323188163747,
%U 2282922216815,16701529748617,126359471558611,987316752551411,7957198067362137
%N a(n) = Sum{k=1 to n} sigma_{n-k+1}(k), where sigma_m(k) = sum{j|k} j^m.
%e a(5) = 1^5 + (1^4 +2^4) + (1^3 +3^3) + (1^2 +2^2 +4^2) + (1^1 +5^1) = 1 + 17 + 28 + 21 + 6 = 73.
%p with(numtheory): s:=proc(n,k) local div: div:=divisors(n): sum(div[j]^k,j=1..tau(n)) end: a:=n->sum(s(i,n-i+1),i=1..n): seq(a(n),n=1..25); # _Emeric Deutsch_, Jul 13 2005
%o (PARI) a(n) = sum(k=1, n, sigma(k, n-k+1)); \\ _Michel Marcus_, Aug 16 2019
%Y Cf. A108699 (with product).
%K nonn
%O 1,2
%A _Leroy Quet_, Jul 07 2005
%E More terms from _Emeric Deutsch_, Jul 13 2005