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 A126388 #16 Feb 16 2025 08:33:04
%S A126388 2,3,6,7,8,9,10,11,12,13,14,15,16,17,22,23,26,27,28,29,30,31,32,33,34,
%T A126388 35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,
%U A126388 58,59,60,61,62,63,64,65,66,67,68,69,72,73,78,79,80,81,86,87,90,91,92
%N A126388 Denominators in a series for the "alternating Euler constant" log(4/Pi).
%C A126388 All n > 1 such that (# of 1's) != (# of 0's) in the base 2 expansion of floor(n/2). The numerators of the series are A126389.
%H A126388 Jonathan Sondow, <a href="http://arXiv.org/abs/math.CA/0211148"> Double integrals for Euler's constant and ln(4/Pi) and an analog of Hadjicostas's formula</a>, arXiv:math/0211148 [math.CA], 2002-2004.
%H A126388 Jonathan Sondow, <a href="https://www.jstor.org/stable/30037385"> Double integrals for Euler's constant and ln(4/Pi) and an analog of Hadjicostas's formula</a>, Amer. Math. Monthly 112 (2005), 61-65.
%H A126388 Jonathan Sondow, <a href="http://arXiv.org/abs/math.NT/0508042">New Vacca-Type Rational Series for Euler's Constant and Its "Alternating" Analog ln(4/Pi)</a>, arXiv:math/0508042 [math.NT], 2005.
%H A126388 Jonathan Sondow, <a href="https://doi.org/10.1007/978-0-387-68361-4_23">New Vacca-Type Rational Series for Euler's Constant and Its "Alternating" Analog ln(4/Pi)</a>, Additive Number Theory, Festschrift In Honor of the Sixtieth Birthday of Melvyn B. Nathanson (D. Chudnovsky and G. Chudnovsky, eds.), Springer, 2010, pp. 331-340.
%H A126388 Eric Weisstein's MathWorld, <a href="https://mathworld.wolfram.com/DigitCount.html">Digit Count</a>.
%F A126388 log(4/Pi) = 1/2 - 1/3 + 2/6 - 2/7 - 1/8 + 1/9 + 1/10 - 1/11 + 1/12 - 1/13 + 3/14 - 3/15 - 2/16 + 2/17 + 2/22 - ...
%e A126388 floor(13/2) = 6 = 110 base 2, which has (# of 1's) = 2 != 1 = (#
%e A126388 of 0's), so 13 is a member.
%t A126388 b[n_] := DigitCount[n,2,1] - DigitCount[n,2,0]; L = {}; Do[If[b[Floor[n/2]] != 0, L = Append[L,n]], {n,2,100}]; L
%Y A126388 Complementary to A066879.
%Y A126388 Cf. A037861, A094640, A094641, A110625, A110626, A126389.
%K A126388 base,nonn
%O A126388 2,1
%A A126388 _Jonathan Sondow_, Jan 01 2007