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A366939 a(n) = Sum_{k=1..n} (-1)^(k-1) * binomial(k+3,4) * floor(n/k).

%I A366939 #11 Oct 29 2023 22:06:35
%S A366939 1,-3,13,-26,45,-70,141,-228,283,-366,636,-879,942,-1232,1914,-2331,
%T A366939 2515,-3090,4226,-5313,5539,-6114,8837,-10558,9988,-11947,15969,
%U A366939 -17705,18256,-20364,26013,-30592,29330,-31874,42222,-47034,44357,-49602,64164,-69115,66637,-74017
%N A366939 a(n) = Sum_{k=1..n} (-1)^(k-1) * binomial(k+3,4) * floor(n/k).
%F A366939 G.f.: 1/(1-x) * Sum_{k>=1} x^k/(1+x^k)^5 = -1/(1-x) * Sum_{k>=1} binomial(k+3,4) * (-x)^k/(1-x^k).
%o A366939 (PARI) a(n) = sum(k=1, n, (-1)^(k-1)*binomial(k+3, 4)*(n\k));
%o A366939 (Python)
%o A366939 from math import isqrt
%o A366939 from sympy import rf
%o A366939 def A366939(n): return ((rf(s:=isqrt(m:=n>>1),3)*(s+1)*((s**2<<2)+13*s+8)<<3)-rf(t:=isqrt(n),5)*(t+1)+sum((((q:=m//w)+1)*(-q*(q+2)*((q**2<<2)+13*q+8)-5*w*(w+1)*((r:=w<<1)+1)*(r+3))<<3) for w in range(1,s+1))+sum(rf(q:=n//w,5)+5*(q+1)*rf(w,4) for w in range(1,t+1)))//120 # _Chai Wah Wu_, Oct 29 2023
%Y A366939 Cf. A024919, A366937, A366938.
%Y A366939 Cf. A365439, A366723.
%K A366939 sign
%O A366939 1,2
%A A366939 _Seiichi Manyama_, Oct 29 2023