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A104385
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Number of distinct partitions of triangular numbers n*(n+1)/2 into 3 parts for n>=1.
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1
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0, 0, 1, 4, 12, 27, 52, 91, 147, 225, 331, 469, 645, 867, 1141, 1474, 1875, 2352, 2914, 3571, 4332, 5208, 6211, 7351, 8640, 10092, 11719, 13534, 15552, 17787, 20254, 22969, 25947, 29205, 32761, 36631, 40833, 45387, 50311, 55624
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| Equals the third column in triangle A104382.
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FORMULA
| a(n) = round((3n^4 + 6n^3 - 33n^2 - 36n + 110)/144) (conjectured). -- Ralf Stephan, Nov 13 2010.
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PROG
| (PARI) {a(n)=if(n<1, 0, polcoeff(polcoeff( prod(i=1, n*(n+1)/2, 1+y*x^i, 1+x*O(x^(n*(n+1)/2))), n*(n+1)/2, x), 3, y))}
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CROSSREFS
| Cf. A000009, A104382.
Sequence in context: A008107 A057306 A047732 * A062479 A007009 A188814
Adjacent sequences: A104382 A104383 A104384 * A104386 A104387 A104388
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KEYWORD
| nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Mar 04 2005
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