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A009640
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Expansion of tan(log(1+tanh(x))).
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0
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0, 1, -1, 2, -10, 46, -226, 1532, -11880, 96136, -882376, 9179312, -102310000, 1223945776, -15941391376, 222827194592, -3303846357120, 52077034777216, -871329939918976, 15375474411183872, -285315305595562240
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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FORMULA
| a(n)=sum(m=0..(n-1)/2, (sum(j=1..2*m+1, j!*2^(2*m-j+1)*(-1)^(m+j+1)* stirling2(2*m+1,j)))*sum(r=2*m+1..n,(stirling1(r,2*m+1)*sum(k=r..n, binomial(k-1,r-1)*k!*2^(n-k)*stirling2(n,k)*(-1)^(r+k)))/r!)). [From Vladimir Kruchinin, Jun 21 2011]
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PROG
| (Maxima)
a(n):=sum((sum(j!*2^(2*m-j+1)*(-1)^(m+j+1)*stirling2(2*m+1, j), j, 1, 2*m+1))*sum((stirling1(r, 2*m+1)*sum(binomial(k-1, r-1)*k!*2^(n-k)*stirling2(n, k)*(-1)^(r+k), k, r, n))/r!, r, 2*m+1, n), m, 0, (n-1)/2); [From Vladimir Kruchinin, Jun 21 2011]
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CROSSREFS
| Sequence in context: A137635 A029706 A191644 * A191684 A081167 A166107
Adjacent sequences: A009637 A009638 A009639 * A009641 A009642 A009643
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KEYWORD
| sign,easy
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AUTHOR
| R. H. Hardin (rhhardin(AT)att.net)
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EXTENSIONS
| Extended with signs Mar 15 1997 by Olivier Gerard.
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