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A005793
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Number of O_1^{2+}(Z)-orbits of Lorentzian modular group.
(Formerly M0078)
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0
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1, 1, 1, 2, 1, 1, 2, 3, 2, 1, 2, 3, 1, 2, 3, 4, 2, 2, 2, 4, 2, 1, 4, 5, 2, 2, 3, 4, 2, 2, 4, 6, 2, 2, 4, 6, 1, 2, 5, 5, 3, 2, 2, 6, 3, 2, 6, 7, 3, 3, 4, 4, 2, 3, 5, 8, 2, 1, 5, 7, 2, 3, 7, 7, 3, 3, 2, 7, 3, 2, 8, 8, 2, 3, 5, 6, 3, 2, 6, 10, 4, 2, 5, 8, 2, 3, 7, 5, 4, 4, 4, 8, 2, 3, 9, 11, 2, 4, 6, 6, 4, 2, 6, 10
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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REFERENCES
| Fox, Glenn J. and Parker, Phillip E.; The Lorentzian modular group and nonlinear lattices. The mathematical heritage of C. F. Gauss, 282-303, World Sci. Publishing, River Edge, NJ, 1991.
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<1, 0, sum(i=0, sqrt(n), if((n-i)%2, 0, sumdiv((n+i*i)/2, d, d>=i&d*d<=(n+i*i)/2))))
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CROSSREFS
| Sequence in context: A014600 A165475 A098280 * A183391 A029346 A030496
Adjacent sequences: A005790 A005791 A005792 * A005794 A005795 A005796
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms and PARI script from Michael Somos, Feb 14, 2002
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