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%I M0368 N0139 #19 Oct 17 2017 03:58:56
%S 1,1,2,2,7,10,20,36,65,118,221,409,776,1463,2788,5328,10222,19714,
%T 38054,73685,142944,277838,540889,1054535,2058537,4023278,7871313,
%U 15414638,30213190,59266422,116343776,228545682,449240740,883570480,1738769611,3423469891,6743730746
%N Number of positive integers <= 2^n of form x^2 + 10 y^2.
%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 and L. P. Schmid, <a href="http://dx.doi.org/10.1090/S0025-5718-1966-0210678-1">Variations on a theorem of Landau. Part I</a>, Math. Comp., 20 (1966), 551-569.
%H <a href="/index/Qua#quadpop">Index entries for sequences related to populations of quadratic forms</a>
%o (PARI) a(n)=local(A);if(n<0,0,A=qfrep([1,0;0,10],2^n);sum(k=1,2^n,A[k]!=0))
%K nonn
%O 0,3
%A _N. J. A. Sloane_
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