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%I M0713 N0263 #35 May 23 2022 09:11:53
%S 1,2,3,5,9,16,29,52,94,175,327,616,1169,2231,4273,8215,15842,30628,
%T 59345,115208,224040,436343,850981,1661663,3248231,6356076,12448925,
%U 24402959,47873156,93984236,184632691,362938014,713852252,1404817026
%N Ramanujan's approximation to population of x^2 + y^2 <= 2^n.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H 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>, Mathematics of Computation 18 (1964), pp. 75-86.
%H <a href="/index/Qua#quadpop">Index entries for sequences related to populations of quadratic forms</a>
%p Digits:=500;
%p K:=.764223653589220662990698731250092328116790541393409514721686673
%p 7496146416587328588384015050131312337219372691207925926341874206467
%p 8084323063315434629380531605171169636177508819961243824994277683469
%p 0516235139218719620569053295644670419176349770659569905712938660289
%p 3858998296105166296089099177929836072973697200640316985128636517347
%p 3921065768550978681981674707359066921; a:=n->round(evalf(K*int(1/sqrt(ln(t)),t=1..2^n))); # Salvador Perez (pies314(AT)hotmail.com), May 08 2005
%Y K = A064533.
%Y Other population sequences for x^2 + y^2: A000050, A000690, A000692.
%K nonn
%O 0,2
%A _N. J. A. Sloane_
%E More terms from Salvador Perez (pies314(AT)hotmail.com), May 08 2005
%E Corrected by _Sean A. Irvine_, Feb 24 2011
%E Name clarified by _Seth A. Troisi_, May 23 2022
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