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 A199638 #8 Mar 30 2012 17:23:03 %S A199638 5,3,21,13,85,53,341,227,1365,909,5461,3637,21845,14563,87381,58253, %T A199638 349525,233013,1398101,932067,5592405,3728269,22369621,14913077, %U A199638 89478485,59652323,357913941,238609293,1431655765,954437173,5726623061,3817748707,22906492245 %N A199638 Last number in row n of triangle A199636. %C A199638 This sequence appears to satisfy a(n) = 4*a(n-2) + a(n-6) - 4*a(n-8). It also appears that a(2n) = A002450(n). %K A199638 nonn %O A199638 4,1 %A A199638 _T. D. Noe_, Nov 14 2011