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 #11 Nov 30 2019 15:15:47
%S 0,2,3,6,0,11,7,14,3,12,11,27,0,23,18,30,0,29,19,36,10,35,23,59,0,28,
%T 30,55,0,66,31,62,14,36,42,81,0,59,42,84,0,74,43,83,18,71,47,123,7,62,
%U 54,84,0,110,66,119,22,60,59,162,0,95,73,126,0,110,67,108,26,138,71
%N Sum of divisors of n that are not of the form 4k+1.
%C a(A004613(n))=0.
%H Vincenzo Librandi, <a href="/A082052/b082052.txt">Table of n, a(n) for n = 1..10000</a>
%F G.f.: Sum_{k>=1} x^(2*k)*(2 + 3*x^k + 4*x^(2*k) + 2*x^(4*k) + x^(5*k))/(1 - x^(4*k))^2. - _Ilya Gutkovskiy_, Sep 12 2019
%t sd[n_]:= Total[Select[Divisors[n], !IntegerQ[(# - 1) / 4]&]]; Array[sd, 100] (* _Vincenzo Librandi_, May 17 2013 *)
%t Table[DivisorSum[n,#&,(!IntegerQ[(#-1)/4]&)],{n,80}] (* _Harvey P. Dale_, Nov 30 2019 *)
%o (PARI) for(n=1,100,print1(sumdiv(n,d,if(d%4!=1,d))","))
%Y Cf. A000203, A050449, A050452, A050460, A078181, A078182, A082053.
%K nonn,easy
%O 1,2
%A _Ralf Stephan_, Apr 02 2003