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A137482
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Number of permutations of n objects such that no two-element subset is preserved.
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0
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1, 1, 0, 2, 14, 54, 304, 2260, 18108, 161756, 1618496, 17815896, 213767080, 2778833992, 38904145344, 583563781424, 9337011390224, 158729175524880, 2857125341582848, 54285381652008736, 1085707629235539936
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| In other words, there are no two objects which the permutation leaves fixed and no two objects that the permutation swaps.
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FORMULA
| E.g.f.=(1+x)exp(-x)exp(-x^2/2)/(1-x).
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EXAMPLE
| a(3)=2 because we have 312 and 231.
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MAPLE
| g:=(1+x)*exp(-x)*exp(-(1/2)*x^2)/(1-x): gser:=series(g, x=0, 25): seq(factorial(n)*coeff(gser, x, n), n=0..20);
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CROSSREFS
| Cf. A000166, A000266.
Sequence in context: A143553 A064363 A067056 * A203576 A178605 A115027
Adjacent sequences: A137479 A137480 A137481 * A137483 A137484 A137485
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KEYWORD
| nonn
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AUTHOR
| Jono Henshaw (jjono(AT)hotmail.com), Apr 22 2008, corrected Apr 30 2008
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