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A253207
a(n) = number of permutations of (1,2,...,n) producible by an ordered quadruple of distinct transpositions.
1
11, 59, 359, 1799, 7091, 22995, 64143, 159093, 359348, 752180, 1478204, 2754752, 4906202, 8402522, 13907394, 22337388, 34933761, 53348561, 79746821, 116926733, 168459797, 238853045, 333735545, 460071495, 626402322, 843120306, 1122776354
OFFSET
4,1
LINKS
FORMULA
a(n) = n!*(1/(384*(n-8)!)+1/(24*(n-7)!)+13/(72*(n-6)!)+1/(5*(n-5)!)+1/(8*(n-4)!)+1/(3*(n-3)!)) for n>=8.
PROG
(PARI) Vec(-x^4*(2*x^8-18*x^7+72*x^6-168*x^5+254*x^4-232*x^3+224*x^2-40*x+11)/(x-1)^9 + O(x^100)) \\ Colin Barker, Dec 30 2014
CROSSREFS
Cf. A000914, for two transpositions, and A253171, for three.
Sequence in context: A249891 A186256 A164299 * A241860 A082884 A193230
KEYWORD
nonn,easy
AUTHOR
Andrew Woods, Dec 28 2014
STATUS
approved