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 A129099 #6 Mar 10 2020 15:32:00
%S A129099 1,4,20,136,1376,22176,591680,26770688,2096125184,289083462144,
%T A129099 71239716616192,31730665042094080,25779103986580017152,
%U A129099 38488216155785101459456,106257557996370396596748288,545336631331873524033714683904
%N A129099 a(n) = Sum_{k=2^(n-1)..2^n-1} A129095(k) for n>=1.
%C A129099 b(n)=A129095(n) obeys the recurrence: b(n) = b(n/2) (n even), b(n) = 2*b(n-1) + b(n-2) (n odd >1), with b(1) = 1.
%F A129099 a(n) = ( A129097(n+1) - A129097(n) )/2.
%t A129099 Block[{e = 16, s}, s = Nest[Append[#1, If[EvenQ[#2], #1[[#2/2]], 2 #1[[-1]] + #1[[-2]] ] ] & @@ {#, Length@ # + 1} &, {1}, 2^e]; Array[Total@ s[[2^# ;; 2^(# + 1) - 1]] &, e, 0] ] (* _Michael De Vlieger_, Mar 10 2020 *)
%o A129099 (PARI)
%Y A129099 Cf. A129095, A129096, A129097, A129098.
%K A129099 easy,nonn
%O A129099 1,2
%A A129099 _Paul D. Hanna_, Apr 11 2007
%E A129099 a(16) from _Michael De Vlieger_, Mar 10 2020