%I A000075 M1078 N0408
%S A000075 0,1,2,4,7,14,23,42,76,139,258,482,907,1717,3269,6257,12020,23171,44762,
%T A000075 86683,168233,327053,636837,1241723,2424228,4738426,9271299,18157441,35591647,
%U A000075 69820626,137068908,269270450,529312241,1041093048,2048825748,4034059456
%N A000075 Number of positive integers <= 2^n of form 2 x^2 + 3 y^2.
%D A000075 D. Shanks and L. P. Schmid, Variations on a theorem of Landau. Part I, 
               Math. Comp., 20 (1966), 551-569.
%D A000075 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000075 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A000075 <a href="Sindx_Qua.html#quadpop">Index entries for sequences related 
               to populations of quadratic forms</a>
%e A000075 a(3)=4 since 2^3=8 and 2=2*1^2, 3=3*1^2, 5=2*1^2+3*1^2, 8=2*2^2.
%o A000075 (PARI) a(n)=if(n<0,0,sum(k=1,2^n,0<sum(y=0,sqrtint(k\3),issquare((k-3*y^2)/
               2))))
%Y A000075 Sequence in context: A079488 A054160 A034426 this_sequence A048248 A056180 
               A000076
%Y A000075 Adjacent sequences: A000072 A000073 A000074 this_sequence A000076 A000077 
               A000078
%K A000075 nonn
%O A000075 0,3
%A A000075 N. J. A. Sloane (njas(AT)research.att.com).