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 A000077 Number of positive integers <= 2^n of form x^2 + 6 y^2. (Formerly M1095 N0417) 0
 1, 1, 2, 4, 8, 13, 24, 42, 76, 140, 257, 483, 907, 1717, 3272, 6261, 12027, 23172, 44769, 86708, 168245, 327073, 636849, 1241720, 2424290, 4738450, 9271396, 18157630, 35591729, 69820804, 137069245, 269270791, 529312776, 1041093937, 2048826229, 4034062310 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES D. Shanks and L. P. Schmid, Variations on a theorem of Landau. Part I, Math. Comp., 20 (1966), 551-569. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS EXAMPLE a(3)=4 since 2^3=8 and 1=1^2, 4=2^2, 6=6*1^2, 7=1^2+6*1^2. PROG (PARI) a(n)=if(n<0, 0, sum(k=1, 2^n, 0

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