This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A120615 #14 Oct 08 2024 07:28:58
%S A120615 0,1,2,5,9,13,19,25,33,42,51,62,74,86,100,114,130,147,164,183,202,223,
%T A120615 245,267,291,316,341,368,395,424,454,484,516,549,582,617,652,689,727,
%U A120615 765,805,845,887,930,973,1018,1064,1110,1158,1206,1256,1307,1358,1411
%N A120615 a(n) = Sum_{k=0..n} floor(phi*floor(k/phi)) where phi = (1+sqrt(5))/2.
%F A120615 a(n) = n*(n-3)/2 + ceiling(n/phi).
%t A120615 Table[Sum[Floor[GoldenRatio*Floor[k/GoldenRatio]],{k,0,n}],{n,54}] (* or *) Table[n(n-3)/2+Ceiling[n/GoldenRatio],{n,54}] (* _James C. McMahon_, Oct 07 2024 *)
%o A120615 (PARI) phi=(1+sqrt(5))/2;a(n)=n*(n-3)/2+ceil(n/phi)
%Y A120615 Cf. A001622, A120613, A120614, A134945.
%K A120615 nonn
%O A120615 1,3
%A A120615 _Benoit Cloitre_, Jun 17 2006