A116807 Number of permutations of length n which avoid the patterns 1234, 2143, 2431.

1, 2, 6, 21, 71, 220, 646, 1835, 5095, 13924, 37627, 100859, 268756, 713023, 1885543, 4974068, 13097587, 34440547, 90467764, 237450167, 622857583, 1633072276, 4280258635, 11215502411, 29381846164, 76961231215, 201564237751

Offset

1,2

Links

Table of n, a(n) for n=1..27.

D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 (2017), Table 2 No 34.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (6,-12,9,-2).

Formula

G.f.: A(x) = -{x(x^8-2x^7-x^6+4x^5-x^4-6x^2+4x-1)}/{(2x-1)(x^2-3x+1)(x-1)}

Crossrefs

Sequence in context: A116749 A116792 A116761 * A294702 A116785 A116801

Adjacent sequences: A116804 A116805 A116806 * A116808 A116809 A116810

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved