%I A000077 M1095 N0417
%S A000077 1,1,2,4,8,13,24,42,76,140,257,483,907,1717,3272,6261,12027,23172,44769,
%T A000077 86708,168245,327073,636849,1241720,2424290,4738450,9271396,18157630,35591729,
%U A000077 69820804,137069245,269270791,529312776,1041093937,2048826229,4034062310
%N A000077 Number of positive integers <= 2^n of form x^2 + 6 y^2
%D A000077 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A000077 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000077 D. Shanks and L. P. Schmid, Variations on a theorem of Landau. Part I, 
               Math. Comp., 20 (1966), 551-569.
%H A000077 <a href="Sindx_Qua.html#quadpop">Index entries for sequences related 
               to populations of quadratic forms</a>
%e A000077 a(3)=4 since 2^3=8 and 1=1^2, 4=2^2, 6=6*1^2, 7=1^2+6*1^2.
%o A000077 (PARI) a(n)=if(n<0,0,sum(k=1,2^n,0<sum(y=0,sqrtint(k\6),issquare(k-6*y^2))))
%Y A000077 Sequence in context: A074467 A018066 A096573 this_sequence A054164 A102704 
               A043774
%Y A000077 Adjacent sequences: A000074 A000075 A000076 this_sequence A000078 A000079 
               A000080
%K A000077 nonn,easy
%O A000077 0,3
%A A000077 N. J. A. Sloane (njas(AT)research.att.com).