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A082970 Number of permutations of length n containing 2 occurrences of 132. 3
4, 23, 107, 464, 1950, 8063, 33033, 134576, 546312, 2212550, 8946454, 36134656, 145831270, 588199815, 2371435125, 9557736480, 38511326040, 155143873170, 624899673690, 2516678580000, 10134353299980, 40805797511622 (list; graph; refs; listen; history; internal format)
OFFSET

4,1

LINKS

T. Mansour and A. Vainshtein, Counting occurrences of 132 in a permutation

FORMULA

a(n)=C(2*n-6, n-2)*(n^3+17*n^2-80*n+80)/(2n(n-1))

PROG

(PARI) a(n)=binomial(2*n-6, n-2)*(n^3+17*n^2-80*n+80)/2/n/(n-1)

CROSSREFS

Sequence in context: A197854 A122738 A038381 * A197868 A017973 A124507

Adjacent sequences:  A082967 A082968 A082969 * A082971 A082972 A082973

KEYWORD

nonn

AUTHOR

Benoit Cloitre (benoit7848c(AT)orange.fr), May 27 2003

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Last modified February 15 15:20 EST 2012. Contains 205823 sequences.