cp's OEIS Frontend

A363804 a(n) = Sum_{d|n, d == 0, 3, or 4 mod 7} d.

%I A363804 #17 Sep 11 2024 17:23:17
%S A363804 0,0,3,4,0,3,7,4,3,10,11,7,0,21,3,4,17,21,0,14,31,11,0,31,25,0,3,53,0,
%T A363804 13,31,36,14,17,42,25,0,38,42,14,0,87,0,15,48,46,0,31,56,35,20,56,53,
%U A363804 21,11,109,3,0,59,77,0,31,94,36,0,80,67,21,3,136,0,49,73,74,28,42,95,42,0,94,84,0,0
%N A363804 a(n) = Sum_{d|n, d == 0, 3, or 4 mod 7} d.
%H A363804 Harvey P. Dale, <a href="/A363804/b363804.txt">Table of n, a(n) for n = 1..1000</a>
%F A363804 G.f.: Sum_{k>0, k == 0, 3 or 4 mod 7} k * x^k/(1 - x^k).
%t A363804 a[n_] := DivisorSum[n, # &, MemberQ[{0, 3, 4}, Mod[#, 7]] &]; Array[a, 100] (* _Amiram Eldar_, Jun 23 2023 *)
%t A363804 sm7[n_]:=Total[Select[Divisors[n],MemberQ[{0,3,4},Mod[#,7]]&]]; Array[sm7,100] (* _Harvey P. Dale_, Sep 11 2024 *)
%o A363804 (PARI) my(N=90, x='x+O('x^N)); concat([0, 0], Vec(sum(k=1, N, [1, 0, 0, 1, 1, 0, 0][k%7+1]*k*x^k/(1-x^k))))
%Y A363804 Cf. A284363, A284444, A284445, A363803.
%Y A363804 Cf. A363801.
%K A363804 nonn,easy
%O A363804 1,3
%A A363804 _Seiichi Manyama_, Jun 23 2023