A116773 Number of permutations of length n which avoid the patterns 1432, 2134, 4132; or avoid the patterns 3124, 4123, 4321.

1, 2, 6, 21, 73, 241, 756, 2276, 6640, 18915, 52911, 145951, 398242, 1077434, 2895486, 7740081, 20603269, 54659533, 144620496, 381823376, 1006354636, 2648774847, 6964087131, 18293818171, 48022224958, 125990960486

Offset

1,2

Links

Table of n, a(n) for n=1..26.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (9,-32,57,-53,24,-4).

Formula

G.f.: A(x) = -{x(4x^5-15x^4+26x^3-20x^2+7x-1)}/{(2x-1)^2(x^2-3x+1)(x-1)^2}

Crossrefs

Sequence in context: A116778 A116787 A294803 * A116741 A116843 A116822

Adjacent sequences: A116770 A116771 A116772 * A116774 A116775 A116776

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved