A116782 Number of permutations of length n which avoid the patterns 3421, 4123, 4231; or avoid the patterns 1342, 3142, 4213.

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

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