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A366813 a(n) = Sum_{d|n} (-1)^(n/d-1) * binomial(d+2,3).

%I A366813 #22 Oct 26 2023 08:32:09
%S A366813 1,3,11,15,36,49,85,95,176,188,287,313,456,479,726,671,970,1024,1331,
%T A366813 1300,1866,1741,2301,2265,2961,2824,3830,3431,4496,4514,5457,5023,
%U A366813 6842,6174,7890,7444,9140,8553,11126,9780,12342,11998,14191,12885,17106,14999,18425
%N A366813 a(n) = Sum_{d|n} (-1)^(n/d-1) * binomial(d+2,3).
%H A366813 Michael De Vlieger, <a href="/A366813/b366813.txt">Table of n, a(n) for n = 1..10000</a>
%F A366813 G.f.: -Sum_{k>=1} (-x)^k/(1-x^k)^4 = Sum_{k>=1} binomial(k+2,3) * x^k/(1+x^k).
%t A366813 Table[DivisorSum[n, (-1)^(n/# - 1)*Binomial[# + 2, 3] &], {n, 56}] (* _Michael De Vlieger_, Oct 25 2023 *)
%o A366813 (PARI) a(n) = sumdiv(n, d, (-1)^(n/d-1)*binomial(d+2, 3));
%Y A366813 Partial sums give A366659.
%Y A366813 Cf. A000593, A365007, A366814.
%K A366813 nonn
%O A366813 1,2
%A A366813 _Seiichi Manyama_, Oct 24 2023