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Search: id:A145454
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| 1, 0, 0, 0, 1, 5, 15, 35, 105, 756, 6510, 46530, 283470, 1667380, 11457446, 99776040, 969295145, 9298091180, 86154691680, 804769174536, 8052676029420, 88489327173660, 1038440150703340, 12501684521410700, 151866259113256611
(list; graph; listen)
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OFFSET
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0,6
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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 4 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 4 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, 4) *a(n-j), j=1..n)) end: seq (a(n), n=0..30);
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CROSSREFS
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Sequence in context: A145133 A143695 A019531 this_sequence A091875 A056413 A032276
Adjacent sequences: A145451 A145452 A145453 this_sequence A145455 A145456 A145457
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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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