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Search: id:A000018
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| A000018 |
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Number of positive integers <= 2^n of form x^2 + 16y^2.
(Formerly M0331 N0126)
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+0
1
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| 1, 1, 2, 2, 4, 8, 13, 25, 44, 83, 152, 286, 538, 1020, 1942, 3725, 7145, 13781, 26627, 51572, 100099, 194633, 379037, 739250, 1443573, 2822186, 5522889, 10818417, 21209278, 41613288, 81705516, 160532194, 315604479, 620834222, 1221918604, 2406183020, 4740461247
(list; graph; listen)
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OFFSET
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0,3
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
D. Shanks and L. P. Schmid, Variations on a theorem of Landau. Part I, Math. Comp., 20 (1966), 551-569.
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LINKS
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Index entries for sequences related to populations of quadratic forms
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PROGRAM
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(PARI) a(n)=local(A); if(n<0, 0, A=qfrep([1, 0; 0, 16], 2^n); sum(k=1, 2^n, A[k]!=0))
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CROSSREFS
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Sequence in context: A104700 A036761 A042979 this_sequence A075126 A098788 A153999
Adjacent sequences: A000015 A000016 A000017 this_sequence A000019 A000020 A000021
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from David W. Wilson (davidwwilson(AT)comcast.net), Feb 07 2000.
Definition corrected by Sean A. Irvine (sairvin(AT)xtra.co.nz), Sep 09 2009
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