A116798 Number of permutations of length n which avoid the patterns 1234, 1342, 1432.

1, 2, 6, 21, 76, 277, 1012, 3702, 13553, 49642, 181885, 666542, 2442922, 8954133, 32821408, 120310377, 441018216, 1616644946, 5926191305, 21723934190, 79634709513, 291922123258, 1070118922286, 3922810609205, 14380129657444, 52714290239405, 193238646748572

Offset

1,2

Links

Colin Barker, Table of n, a(n) for n = 1..1000

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 202.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (7,-15,11,-3).

Formula

G.f.: x*(1 - 2*x)*(1 - 3*x + x^2) / (1 - 7*x + 15*x^2 - 11*x^3 + 3*x^4).

a(n) = 7*a(n-1) - 15*a(n-2) + 11*a(n-3) - 3*a(n-4) for n>4. - Colin Barker, Oct 23 2017

Prog

(PARI) Vec(x*(1 - 2*x)*(1 - 3*x + x^2) / (1 - 7*x + 15*x^2 - 11*x^3 + 3*x^4) + O(x^30)) \\ Colin Barker, Oct 23 2017

Crossrefs

Sequence in context: A116782 A112091 A108146 * A279560 A116821 A116772

Adjacent sequences: A116795 A116796 A116797 * A116799 A116800 A116801

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved