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Search: id:A145453
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| 1, 0, 0, 1, 4, 10, 30, 175, 1176, 7084, 42120, 286605, 2270180, 19213766, 166326524, 1497096055, 14374680880, 147259920760, 1582837679056, 17659771122969, 204674606377140, 2473357218561250, 31148510170120420, 407154732691440811
(list; graph; listen)
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OFFSET
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0,5
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COMMENT
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a(n) is the number of ways of placing n labeled balls into indistinguishable boxes, where in each filled box 3 balls are seen at the top.
a(n) is also the number of forests of labeled rooted trees of height at most 1, with n labels, where each root contains 3 labels.
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LINKS
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N. J. A. Sloane, Transforms
Index entries for sequences related to rooted trees
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MAPLE
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a:= proc(n) option remember; local j; `if` (n=0, 1, add (binomial (n-1, j-1) *binomial(j, 3) *a(n-j), j=1..n)) end: seq (a(n), n=0..30);
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CROSSREFS
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Cf. 3rd column of A145460, A143398.
Sequence in context: A114946 A001551 A067142 this_sequence A034730 A095127 A006342
Adjacent sequences: A145450 A145451 A145452 this_sequence A145454 A145455 A145456
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KEYWORD
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nonn
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AUTHOR
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Alois P. Heinz (heinz(AT)hs-heilbronn.de), Oct 10 2008
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