A116824 Number of permutations of length n which avoid the patterns 1234, 3412, 3421.

1, 2, 6, 21, 73, 229, 634, 1562, 3481, 7132, 13622, 24531, 42033, 69031, 109306, 167680, 250193, 364294, 519046, 725345, 996153, 1346745, 1794970, 2361526, 3070249, 3948416, 5027062, 6341311, 7930721, 9839643

Offset

1,2

Links

Table of n, a(n) for n=1..30.

D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 (2017), Table 2 No 64.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).

Formula

G.f.: A(x) = -{x(4x^6-2x^5+17x^4-14x^3+13x^2-5x+1)}/{(x-1)^7}

a(n) = (7n^6 - 78n^5 + 460n^4 - 1500n^3 + 2953n^2 - 2922n + 1440)/360. - Franklin T. Adams-Watters, Sep 16 2006

Crossrefs

Sequence in context: A116762 A116803 A116829 * A116789 A116783 A116739

Adjacent sequences: A116821 A116822 A116823 * A116825 A116826 A116827

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved