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 A123779 #7 Feb 15 2025 15:24:55 %S A123779 1,1,21,67,849,3185,39868,162562,2027829 %N A123779 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 4 which is symmetric after a rotation by 180 degrees. %Y A123779 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123779 nonn %O A123779 1,3 %A A123779 _Søren Eilers_, Oct 29 2006