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Search: id:A115076
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| A115076 |
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Number of 2 X 2 symmetric matrices over Z(n) having determinant 1. |
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+0
2
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| 1, 4, 6, 12, 30, 24, 42, 48, 54, 120, 110, 72, 182, 168, 180, 192, 306, 216, 342, 360, 252, 440, 506, 288, 750, 728, 486, 504, 870, 720, 930, 768, 660, 1224, 1260, 648, 1406, 1368, 1092, 1440, 1722, 1008, 1806, 1320, 1620, 2024, 2162, 1152, 2058, 3000
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(1)=1 because the matrix of all zeros has determinant 0, but 0=1 (mod 1).
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MATHEMATICA
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Table[cnt=0; Do[m={{a, b}, {b, c}}; If[Det[m, Modulus->n]==1, cnt++ ], {a, 0, n-1}, {b, 0, n-1}, {c, 0, n-1}]; cnt, {n, 50}]
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CROSSREFS
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Cf. A000056 (order of the group SL(2, Z_n)).
Sequence in context: A037100 A095969 A090608 this_sequence A126259 A092320 A056495
Adjacent sequences: A115073 A115074 A115075 this_sequence A115077 A115078 A115079
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KEYWORD
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mult,nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), Jan 12 2006
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