A116782 - OEIS

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A116782

Number of permutations of length n which avoid the patterns 3421, 4123, 4231; or avoid the patterns 1342, 3142, 4213.

0

1, 2, 6, 21, 76, 275, 991, 3563, 12800, 45976, 165141, 593184, 2130737, 7653715, 27492557, 98754742, 354732286, 1274217137, 4577055240, 16441024023, 59057026159, 212135955587, 762003551500, 2737156984928, 9832012391033

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..25.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (6,-11,9,-2).

FORMULA

G.f.: A(x) = -{x(x-1)^2(2x-1)}/{2x^4-6x-9x^3+1+11x^2}

CROSSREFS

Sequence in context: A116819 A294819 A294820 * A112091 A108146 A116798

Adjacent sequences: A116779 A116780 A116781 * A116783 A116784 A116785

KEYWORD

nonn,easy

AUTHOR

Lara Pudwell, Feb 26 2006

STATUS

approved