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 A010737 #11 Mar 30 2012 18:38:36 %S A010737 4,6,9,13,19,27,39,55,79,111,159,223,319,447,639,895,1279,1791,2559, %T A010737 3583,5119,7167,10239,14335,20479,28671,40959,57343,81919,114687, %U A010737 163839,229375,327679,458751,655359 %N A010737 a(n) = 2*a(n-2) + 1. %F A010737 a(2n)=5*2^n-1 and a(2n+1)=7*2^n-1 or a(n)=(6-(-1)^n)*2^floor(n/2)-1 - _Benoit Cloitre_, May 04 2003 %p A010737 A010737 := proc(n) options remember; if n <= 1 then 2*n+4 else 2*A010737(n-2)+1; fi end; %o A010737 (PARI) a(n)=(6-(-1)^n)*2^floor(n/2)-1 %K A010737 nonn,easy %O A010737 0,1 %A A010737 _N. J. A. Sloane_, Ulrich Hund (hund(AT)math.tu-berlin.de)