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A116755
Number of permutations of length n which avoid the patterns 1234, 2431, 3412.
0
1, 2, 6, 21, 71, 213, 561, 1317, 2809, 5536, 10220, 17865, 29823, 47867, 74271, 111897, 164289, 235774, 331570, 457901, 622119, 832833, 1100045, 1435293, 1851801, 2364636, 2990872, 3749761, 4662911, 5754471
OFFSET
1,2
FORMULA
G.f.: A(x) = -{x(x^6-4x^5+15x^4-14x^3+13x^2-5x+1)}/{(x-1)^7}
a(n) = (7n^6 - 45n^5 + 175n^4 - 315n^3 + 538n^2 - 360n + 720)/720. - Franklin T. Adams-Watters, Sep 16 2006
CROSSREFS
Sequence in context: A116759 A116835 A294725 * A116833 A116808 A294726
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved