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A001767
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Genus of modular group GAMMA_n. Or, genus of modular curve CHI(n).
(Formerly M2459 N0976)
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0
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0, 0, 0, 0, 1, 3, 5, 10, 13, 26, 25, 50, 49, 73, 81, 133, 109, 196, 169, 241, 241, 375, 289, 476, 421, 568, 529, 806, 577, 1001, 833, 1081, 1009, 1393, 1081, 1768, 1441, 1849, 1633, 2451, 1729, 2850, 2281, 2809, 2641, 3773, 2689, 4215, 3301, 4321, 3865
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,6
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REFERENCES
| R. C. Gunning, Lectures on Modular Forms. Princeton Univ. Press, Princeton, NJ, 1962, p. 15.
B. Iversen, Hyperbolic Geometry, Cambridge Univ. Press, 1992, see p. 238.
Russian Encyclopedia of Mathematics, Vol. 3, page 931.
B. Schoeneberg, Elliptic Modular Functions, Springer-Verlag, NY, 1974, p. 94.
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
| Index entries for sequences related to modular groups
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PROG
| (PARI) {a(n)=if(n<3, 0, 1+n^2*(n-6)/24*prod(p=2, n, if(isprime(p)&(n%p==0), 1-1/p^2, 1)))} /* Michael Somos May 19 2004 */
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CROSSREFS
| Sequence in context: A031878 A160792 A137395 * A048214 A195094 A001841
Adjacent sequences: A001764 A001765 A001766 * A001768 A001769 A001770
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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