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 A027120 #9 Dec 29 2023 23:15:49 %S A027120 2,7,20,56,155,429,1188,3298,9181,25634,71781,201569,567538,1601971, %T A027120 4532460,12851882,36516613,103955432,296471643,846932919,2423256440, %U A027120 6943726380,19924638557,57247669927,164688166948,474323305547 %N A027120 a(n) = A027113(n, 2n-2). %Y A027120 Cf. A027113. %K A027120 nonn %O A027120 2,1 %A A027120 _Clark Kimberling_