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Search: id:A115225
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| A115225 |
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Number of 3 X 3 symmetric matrices over Z(n) having nonzero determinant. |
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3
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| 0, 28, 468, 2688, 12400, 37260, 100548, 215040, 454896, 883900, 1609300, 2618496, 4453488, 6913900, 10548900, 15138816, 22713088, 31256604, 44563284, 59459200, 81302760, 107538508, 141587908, 178808832, 232500000, 295476220, 368465760
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OFFSET
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1,2
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FORMULA
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a(n)=n^6-A115223(n). For prime n, a(n)=(n^3-1)(n-1)n^2.
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MATHEMATICA
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Table[cnt=0; Do[m={{a, b, c}, {b, d, e}, {c, e, f}}; If[Det[m, Modulus->n]>0, cnt++ ], {a, 0, n-1}, {b, 0, n-1}, {c, 0, n-1}, {d, 0, n-1}, {e, 0, n-1}, {f, 0, n-1}]; cnt, {n, 2, 20}]
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CROSSREFS
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Cf. A115222 (number of 3 X 3 matrices over Z(n) having nonzero determinant).
Sequence in context: A160060 A115226 A086782 this_sequence A140107 A028170 A076172
Adjacent sequences: A115222 A115223 A115224 this_sequence A115226 A115227 A115228
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KEYWORD
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nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), Jan 16 2006
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