A116755 Number of permutations of length n which avoid the patterns 1234, 2431, 3412.

1, 2, 6, 21, 71, 213, 561, 1317, 2809, 5536, 10220, 17865, 29823, 47867, 74271, 111897, 164289, 235774, 331570, 457901, 622119, 832833, 1100045, 1435293, 1851801, 2364636, 2990872, 3749761, 4662911, 5754471

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 25.

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.: -x*(x^6-4*x^5+15*x^4-14*x^3+13*x^2-5*x+1)/(x-1)^7.

a(n) = (7*n^6 - 45*n^5 + 175*n^4 - 315*n^3 + 538*n^2 - 360*n + 720)/720. - Franklin T. Adams-Watters, Sep 16 2006

Crossrefs

Sequence in context: A116759 A116835 A294725 * A116833 A116808 A294726

Adjacent sequences: A116752 A116753 A116754 * A116756 A116757 A116758

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved