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 A123785 #11 Sep 16 2018 09:56:36 %S A123785 1,3,5,16,36,124,287,1043,2573,9448,24161,89827,235902,886047,2372494, %T A123785 8968829,24410414,92783928,255723571,976331352 %N A123785 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 4 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees. %C A123785 The base block is not counted among the n and must be the only block in the bottom layer of the building. %Y A123785 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123785 nonn %O A123785 1,2 %A A123785 _Søren Eilers_, Oct 29 2006 %E A123785 a(14)-a(20) from _Søren Eilers_, Sep 16 2018