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 A000692 M2311 N0913 #40 Aug 06 2023 23:33:59
%S A000692 1,3,4,5,9,15,27,50,92,171,322,610,1161,2220,4260,8201,15828,30622,
%T A000692 59362,115287,224260,436871,852161,1664196,3253531,6366973,12471056,
%U A000692 24447507,47962236,94161474,184983976,363632192,715220838,1407510311
%N A000692 An approximation to population of x^2 + y^2 <= 2^n.
%D A000692 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A000692 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A000692 D. Hare, <a href="http://www.plouffe.fr/simon/constants/landau.txt">The constant c</a> [Dave Hare, May 21 1996].
%H A000692 D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1964-0159174-9">The second-order term in the asymptotic expansion of B(x)</a>, Math. Comp., 18 (1964), 75-86.
%H A000692 <a href="/index/Qua#quadpop">Index entries for sequences related to populations of quadratic forms</a>.
%F A000692 a(n) = (b*2^n / sqrt(n*log(2))) * (1 + c/(n*log(2))) where b=0.764223654... is the Landau-Ramanujan constant (A064533) and c=0.5819486593... is the second-order Landau-Ramanujan constant (A227158) given by c = (1/2) * (1-log(Pi*e^gamma/(2*L))) - (1/4) * D(1) where D(s) = (d/ds)(log(Product_{p prime == 3 (mod 4)} 1/(1-p^(-2*s)))) and L is the Lemniscate constant (A064853) [see (12) in Shanks]. - _Sean A. Irvine_, Feb 25 2011
%Y A000692 Cf. A064533.
%Y A000692 Other population sequences for x^2 + y^2: A000050, A000690, A000691.
%K A000692 nonn
%O A000692 0,2
%A A000692 _N. J. A. Sloane_
%E A000692 More terms from _Sean A. Irvine_, Feb 24 2011
%E A000692 Name clarified by _Seth A. Troisi_, May 23 2022