cp's OEIS Frontend

A366968 a(n) = Sum_{k=3..n} floor(n/k).

%I A366968 #14 Oct 30 2023 11:12:43
%S A366968 0,0,1,2,3,5,6,8,10,12,13,17,18,20,23,26,27,31,32,36,39,41,42,48,50,
%T A366968 52,55,59,60,66,67,71,74,76,79,86,87,89,92,98,99,105,106,110,115,117,
%U A366968 118,126,128,132,135,139,140,146,149,155,158,160,161,171,172,174,179,184
%N A366968 a(n) = Sum_{k=3..n} floor(n/k).
%F A366968 G.f.: 1/(1-x) * Sum_{k>=1} x^(3*k)/(1-x^k) = 1/(1-x) * Sum_{k>=3} x^k/(1-x^k).
%F A366968 a(n) = A006218(n)-n-floor(n/2). - _Chai Wah Wu_, Oct 30 2023
%o A366968 (PARI) a(n) = sum(k=3, n, n\k);
%o A366968 (Python)
%o A366968 from math import isqrt
%o A366968 def A366968(n): return -(s:=isqrt(n))**2+(sum(n//k for k in range(3,s+1))<<1)+n+(n>>1) if n>3 else int(n>2) # _Chai Wah Wu_, Oct 30 2023
%Y A366968 Column k=3 of A134867.
%Y A366968 Partial sums of A023645.
%Y A366968 Cf. A006218, A366969, A366970, A366971.
%K A366968 nonn,easy
%O A366968 1,4
%A A366968 _Seiichi Manyama_, Oct 30 2023