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A000018 Number of positive integers <= 2^n of form x^2 + 16*y^2.
(Formerly M0331 N0126)
1
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; 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.
PROG
(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))
CROSSREFS
Sequence in context: A039941 A036761 A042979 * A357307 A306604 A354784
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from David W. Wilson, Feb 07 2000
Definition corrected by Sean A. Irvine, Sep 09 2009
STATUS
approved

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Last modified March 29 04:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)