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A116778
Number of permutations of length n which avoid the patterns 2431, 3124, 3421.
0
1, 2, 6, 21, 73, 240, 754, 2309, 6987, 21036, 63202, 189723, 569311, 1708100, 5124492, 15373695, 46121335, 138364290, 415093192, 1245279935, 3735840201, 11207521038, 33622563592, 100867691301, 302603074477, 907809224054
OFFSET
1,2
FORMULA
G.f.: A(x) = -{(3x^5-9x^4+11x^3-11x^2+5x-1)x}/{(x-1)^3(3x-1)(x^2-x+1)}
CROSSREFS
Sequence in context: A294802 A116788 A294695 * A116787 A294803 A116773
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved