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 A120140 #11 May 13 2023 19:21:03
%S A120140 13,19,29,43,65,97,146,219,328,492,738,1107,1661,2491,3737,5605,8408,
%T A120140 12612,18918,28377,42565,63848,95772,143658,215487,323230,484845,
%U A120140 727268,1090902,1636353,2454529,3681794,5522691,8284036,12426054,18639081
%N A120140 a(n) = 13 + floor(Sum_{j=1..n-1} a(j)/2).
%H A120140 G. C. Greubel, <a href="/A120140/b120140.txt">Table of n, a(n) for n = 1..1000</a>
%t A120140 a[n_]:= a[n]= 13 +Quotient[Sum[a[k], {k,n-1}], 2];
%t A120140 Table[a[n], {n,60}] (* _G. C. Greubel_, May 11 2023 *)
%o A120140 (SageMath)
%o A120140 @CachedFunction
%o A120140 def A120140(n): return 13 + sum(A120140(k) for k in range(1,n))//2
%o A120140 [A120140(n) for n in range(1,60)] # _G. C. Greubel_, May 11 2023
%Y A120140 Cf. A073941, A072493, A112088, A120134 - A120139, A120141 - A120209.
%K A120140 nonn
%O A120140 1,1
%A A120140 _Graeme McRae_, Jun 10 2006