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 A000021 Number of positive integers <= 2^n of form x^2 + 12 y^2. (Formerly M0357 N0134) 2
 1, 1, 2, 2, 6, 9, 17, 30, 54, 98, 183, 341, 645, 1220, 2327, 4451, 8555, 16489, 31859, 61717, 119779, 232919, 453584, 884544, 1727213, 3376505, 6607371, 12942012, 25371540, 49777187, 97731027, 192010355, 377475336, 742512992, 1461352025, 2877572478, 5668965407 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES 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 Delbert L. Johnson, Table of n, a(n) for n = 0..45 D. Shanks and L. P. Schmid, Variations on a theorem of Landau. Part I, Math. Comp., 20 (1966), 551-569. Index entries for sequences related to populations of quadratic forms EXAMPLE a(4)=6 since 2^4=16 and 1=1^2, 4=2^2, 9=3^2, 12=12*1^2, 13=1^2+12*1^2, 16=4^2. PROG (PARI) a(n)=if(n<0, 0, sum(k=1, 2^n, 0 0] -- Reinhard Zumkeller, Apr 16 2012 CROSSREFS Cf. A000196, A010052, A272933. Sequence in context: A021819 A359896 A339426 * A367718 A000022 A034805 Adjacent sequences: A000018 A000019 A000020 * A000022 A000023 A000024 KEYWORD nonn AUTHOR N. J. A. Sloane EXTENSIONS More terms from David W. Wilson, Feb 07 2000 STATUS approved

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Last modified November 30 03:37 EST 2023. Contains 367452 sequences. (Running on oeis4.)