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A258496
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Number of words of length 2n such that all letters of the nonary alphabet occur at least once and are introduced in ascending order and which can be built by repeatedly inserting doublets into the initially empty word.
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2
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4862, 629850, 47432550, 2728352253, 133216751525, 5829093450180, 236006398327050, 9025008152896320, 330547676678287002, 11710509049983422030, 404211829411082901714, 13667296618312167097605, 454559414725395785663741, 14918526141220986683667840
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OFFSET
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9,1
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LINKS
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Alois P. Heinz, Table of n, a(n) for n = 9..650
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FORMULA
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a(n) ~ 32^n / (246960*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Jun 01 2015
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MAPLE
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A:= proc(n, k) option remember; `if`(n=0, 1, k/n*
add(binomial(2*n, j)*(n-j)*(k-1)^j, j=0..n-1))
end:
T:= (n, k)-> add((-1)^i*A(n, k-i)/(i!*(k-i)!), i=0..k):
a:= n-> T(n, 9):
seq(a(n), n=9..25);
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CROSSREFS
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Column k=9 of A256117.
Sequence in context: A124088 A244106 A264182 * A258397 A215549 A295442
Adjacent sequences: A258493 A258494 A258495 * A258497 A258498 A258499
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KEYWORD
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nonn
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AUTHOR
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Alois P. Heinz, May 31 2015
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STATUS
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approved
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