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 A191636 #21 Sep 08 2022 08:45:57
%S A191636 3,5,12,36,113,372,1260,4369,15420,55188,199728,729444,2684354,
%T A191636 9942053,37025580,138547332,520602096,1963413621,7429132620,
%U A191636 28192605840,107269427100,409120605684,1563749870614,5988829291716,22977549119237,88305875046480,339894311499660
%N A191636 a(n) = floor((-1 + 4^n)/(-1 + 2*n)).
%H A191636 Vincenzo Librandi, <a href="/A191636/b191636.txt">Table of n, a(n) for n = 1..1000</a>
%t A191636 f[n_] := Floor[(-1+4^n)/(-1+2 n)]
%t A191636 Table[f[n], {n, 1, 40}] (* A191636 *)
%o A191636 (Magma) [Floor((-1+4^n)/(-1+2*n)): n in [1..30] ];// _Vincenzo Librandi_, Sep 10 2011
%o A191636 (Maxima) A191636(n):=floor((-1+4^n)/(-1+2*n))$ makelist(A191636(n),n,1,30); /* _Martin Ettl_, Oct 25 2012 */
%Y A191636 Cf. A191637.
%K A191636 nonn
%O A191636 1,1
%A A191636 _Clark Kimberling_, Jun 09 2011