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 A023664 #17 Jun 16 2019 17:52:30 %S A023664 2,11,30,63,117,194,298,434,604,816,1072,1375,1735,2151,2628,3172, %T A023664 3783,4471,5237,6083,7019,8042,9162,10382,11702,13136,14680,16339, %U A023664 18122,20025,22061,24230,26532,28985,31580,34325,37228,40284,43509,46900 %N A023664 Convolution of the lower and upper Wythoff sequences (A000201 and A001950). %o A023664 (PARI) a(n) = my(phi = (1+sqrt(5))/2); sum(k=1, n, floor(k*phi)*floor((n-k+1)*phi^2)); \\ _Michel Marcus_, Jun 10 2019 %Y A023664 Cf. A000201, A001950. %K A023664 nonn %O A023664 1,1 %A A023664 _Clark Kimberling_ %E A023664 Missing a(13) = 1735 inserted by _Sean A. Irvine_, Jun 09 2019