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Search: id:A000074
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| A000074 |
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Number of odd integers <= 2^n of form x^2 + y^2.
(Formerly M1077 N0407)
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+0
1
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| 1, 1, 1, 2, 4, 7, 13, 25, 43, 83, 157, 296, 564, 1083, 2077, 4006, 7733, 14968, 29044, 56447, 109864, 214197, 418080, 816907, 1598040, 3129063, 6132106, 12027122, 23606527, 46366165, 91127332, 179207074, 352615528, 694182554, 1367278759
(list; graph; listen)
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OFFSET
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1,4
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REFERENCES
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D. Shanks, The second-order term in the asymptotic expansion of B(x), Math. Comp., 18 (1964), 75-86.
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).
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LINKS
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Index entries for sequences related to populations of quadratic forms
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EXAMPLE
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a(4)=4 since 2^4=16 and 1=1^2, 5=1^2+2^2, 9=3^2, 13=2^2+3^2.
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PROGRAM
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(PARI) a(n)=if(n<0, 0, sum(k=1, 2^(n-1), 0<sum(y=0, sqrtint(2*k-1), issquare(2*k-1-y^2))))
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CROSSREFS
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Sequence in context: A102112 A102113 A034440 this_sequence A079958 A018082 A018083
Adjacent sequences: A000071 A000072 A000073 this_sequence A000075 A000076 A000077
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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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9 more terms. Sean A. Irvine (sairvin(AT)xtra.co.nz), Sep 14 2009
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