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 A086221 #9 Nov 15 2021 17:27:06
%S A086221 13,58,244,1000,4048,16288,65344,261760,1047808,4192768,16774144,
%T A086221 67102720,268423168,1073717248,4294918144,17179770880,68719280128,
%U A086221 274877513728,1099510841344,4398044938240,17592182898688,70368737886208
%N A086221 Bisection of A086652.
%C A086221 (a(n)-2^(n-1))/2 = A006516(n+1).
%H A086221 Harvey P. Dale, <a href="/A086221/b086221.txt">Table of n, a(n) for n = 1..1000</a>
%F A086221 a(n) = 2^(2n+2)-3*2^(n-1).
%F A086221 a(n+1) = 4*a(n)+3*2^n.
%t A086221 Table[2^(2n+2)-3*2^(n-1),{n,30}] (* or *) nxt[{n_,a_}]:={n+1,4a+3*2^n}; NestList[nxt,{1,13},30][[All,2]] (* _Harvey P. Dale_, Nov 15 2021 *)
%Y A086221 Cf. A006516, A086652.
%K A086221 nonn,easy
%O A086221 1,1
%A A086221 _Marco Matosic_, Jul 27 2003
%E A086221 Edited and extended by _David Wasserman_, Feb 17 2005