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 A191637 #18 Sep 08 2022 08:45:57
%S A191637 1,3,9,28,93,315,1092,3855,13797,49932,182361,671088,2485513,9256395,
%T A191637 34636833,130150524,490853405,1857283155,7048151460,26817356775,
%U A191637 102280151421,390937467653,1497207322929,5744387279809,22076468761620,84973577874915,327534518354217
%N A191637 a(n) = floor((1 + 4^n)/(1 + 2*n)).
%H A191637 Vincenzo Librandi, <a href="/A191637/b191637.txt">Table of n, a(n) for n = 1..1000</a>
%t A191637 f[n_] := Floor[(1+4^n)/(1+2 n)]
%t A191637 Table[f[n], {n, 1, 40}] (* A191637 *)
%o A191637 (Magma) [Floor((1+4^n)/(1+2*n)): n in [1..30] ]; // _Vincenzo Librandi_, Sep 10 2011
%o A191637 (Maxima) A191637(n):=floor((1+4^n)/(1+2*n))$ makelist(A191637(n),n,1,30); /* _Martin Ettl_, Oct 25 2012 */
%Y A191637 Cf. A191636.
%K A191637 nonn
%O A191637 1,2
%A A191637 _Clark Kimberling_, Jun 09 2011