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 A116601 #23 Oct 13 2022 15:28:02
%S A116601 0,0,0,1,1,2,3,5,7,11,15,22,31,45,63,90,127,181,255,362,511,724,1023,
%T A116601 1448,2047,2896,4095,5792,8191,11585,16383,23170,32767,46340,65535,
%U A116601 92681,131071,185363,262143,370727,524287,741455,1048575,1482910,2097151,2965820,4194303,5931641
%N A116601 a(0) = a(1) = 0; for n >= 2, a(n) = floor(sqrt(2^(n-2)-1)).
%C A116601 Numbers k such that k^2 is the largest square less than the next power of 2. - _Hugo Pfoertner_, Sep 30 2022
%H A116601 G. C. Greubel, <a href="/A116601/b116601.txt">Table of n, a(n) for n = 0..440</a>
%t A116601 Join[{0, 0}, Table[Floor[Sqrt[2^(n - 2) - 1]], {n, 2, 50}]] (* _G. C. Greubel_, Oct 28 2017 *)
%o A116601 (Python)
%o A116601 from math import isqrt
%o A116601 def A116601(n): return isqrt((1<<n-2)-1) if n > 1 else 0 # _Chai Wah Wu_, Oct 13 2022
%Y A116601 Cf. A002193, A357754.
%K A116601 nonn
%O A116601 0,6
%A A116601 _Roger L. Bagula_, Mar 28 2006
%E A116601 Edited by _N. J. A. Sloane_, May 10 2007