A116848 Number of permutations of length n which avoid the patterns 231, 51234.

1, 2, 5, 14, 41, 119, 336, 927, 2527, 6870, 18717, 51155, 140120, 384147, 1053147, 2886182, 7906953, 21657679, 59318944, 162475127, 445041287, 1219069014, 3339354501, 9147387195, 25057021032, 68637206987, 188013260835, 515011570790, 1410735630289

Offset

1,2

Links

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

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (6,-14,17,-10,4).

Formula

G.f.: x*(1 - 4*x + 7*x^2 - 5*x^3 + 3*x^4) / (1 - 6*x + 14*x^2 - 17*x^3 + 10*x^4 - 4*x^5).

a(n) = 6*a(n-1) - 14*a(n-2) + 17*a(n-3) - 10*a(n-4) + 4*a(n-5) for n>5. - Colin Barker, Nov 01 2017

Prog

(PARI) Vec(x*(1 - 4*x + 7*x^2 - 5*x^3 + 3*x^4) / (1 - 6*x + 14*x^2 - 17*x^3 + 10*x^4 - 4*x^5) + O(x^40)) \\ Colin Barker, Nov 01 2017

Crossrefs

Sequence in context: A038989 A116850 A116847 * A370800 A122055 A244885

Adjacent sequences: A116845 A116846 A116847 * A116849 A116850 A116851

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved