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A093345
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n! * {1 + Sum[i=1..n, 1/i*Sum(j=0..i-1, 1/j!)]}.
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2
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1, 2, 6, 23, 108, 605, 3956, 29649, 250892, 2367629, 24662700, 281153801, 3482350724, 46572620757, 668943488084, 10271127486065, 167892667249116, 2911049382788189, 53365747562592092, 1031352659792534169
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Number of {12,2*1}-avoiding signed permutations in the hyperoctahedral group B_n.
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LINKS
| T. Mansour and J. West, Avoiding 2-letter signed patterns.
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FORMULA
| E.g.f.: (exp(1)*(Ei(1, 1-x)-Ei(1, 1))+1)/(1-x). a(n) = n!*(1+Sum(A000522(i-1)/i!, i =1..n)). - Vladeta Jovovic (vladeta(AT)eunet.rs), Apr 27 2004
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PROG
| (PARI) a(n)=n!+n!*sum(i=1, n, 1/i*sum(j=0, i-1, 1/j!))
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CROSSREFS
| Cf. A000774.
Cf. A000522, A093344.
Contribution from Johannes W. Meijer (meijgia(AT)hotmail.com), Oct 16 2009: (Start)
Equals row sums of A165675.
(End)
Sequence in context: A155857 A071076 A112501 * A002136 A205802 A117226
Adjacent sequences: A093342 A093343 A093344 * A093346 A093347 A093348
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KEYWORD
| nonn
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AUTHOR
| Ralf Stephan, Apr 26 2004
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