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Search: id:A000003
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| A000003 |
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Number of classes of primitive binary forms of discriminant D = -4n; or equivalently class number of quadratic order of discriminant D = -4n.
(Formerly M0196 N0073)
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+0
10
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| 1, 1, 1, 1, 2, 2, 1, 2, 2, 2, 3, 2, 2, 4, 2, 2, 4, 2, 3, 4, 4, 2, 3, 4, 2, 6, 3, 2, 6, 4, 3, 4, 4, 4, 6, 4, 2, 6, 4, 4, 8, 4, 3, 6, 4, 4, 5, 4, 4, 6, 6, 4, 6, 6, 4, 8, 4, 2, 9, 4, 6, 8, 4, 4, 8, 8, 3, 8, 8, 4, 7, 4, 4, 10, 6, 6, 8, 4, 5, 8, 6, 4, 9, 8, 4, 10, 6, 4, 12, 8, 6, 6, 4, 8, 8, 8, 4, 8, 6, 4
(list; graph; listen)
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OFFSET
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1,5
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REFERENCES
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H. Cohen, Course in Computational Alg. No. Theory, Springer, 1993, p. 514.
Fell, Harriet; Newman, Morris; Ordman, Edward; Tables of genera of groups of linear fractional transformations. J. Res. Nat. Bur. Standards Sect. B 67B 1963 61-68.
D. Shanks, Generalized Euler and class numbers, Math. Comp. 21 (1967), 689-694; 22 (1968), 699.
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LINKS
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N. J. A. Sloane, Table of n, a(n) for n = 1..5000
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PROGRAM
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(MAGMA) O1 := MaximalOrder(QuadraticField(D)); _, f := IsSquare(D div Discriminant(O1)); ClassNumber(sub<O1|f>);
(PARI) a(n)=qfbclassno(-4*n)
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CROSSREFS
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Adjacent sequences: A000001 A000002 this_sequence A000004 A000005 A000006
Sequence in context: A029420 A029405 A029350 this_sequence A029395 A029282 A029286
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KEYWORD
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nonn,nice,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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