A116743 Number of permutations of length n which avoid the patterns 3421, 4123, 4213.

1, 2, 6, 21, 75, 267, 950, 3384, 12065, 43034, 153524, 547744, 1954328, 6973114, 24880601, 88776363, 316763410, 1130246720, 4032847433, 14389658085, 51343944371, 183201075822, 653682454214, 2332414030833, 8322321077596

Offset

1,2

Links

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

D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 [math.CO] (2017), Table 2 No 179.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (7,-17,21,-16,6,-1)

Formula

G.f.: A(x) = -{x(x^3-2x^2+3x-1)(x-1)^2}/{(x^2-x+1)(x^4-5x^3+10x^2-6x+1)}

Crossrefs

Sequence in context: A116751 A116823 A289597 * A294816 A263790 A247416

Adjacent sequences: A116740 A116741 A116742 * A116744 A116745 A116746

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved