login
A116710
Number of permutations of length n which avoid the patterns 1423, 3421.
1
1, 2, 6, 22, 86, 337, 1299, 4910, 18228, 66640, 240550, 859295, 3043525, 10705182, 37441618, 130351650, 452119862, 1563402141, 5392828631, 18564966510, 63807048144, 219015409556, 750968486726, 2572756726459, 8808011192329, 30138217809470, 103077794599470
OFFSET
1,2
LINKS
Darla Kremer and Wai Chee Shiu, Finite transition matrices for permutations avoiding pairs of length four patterns, Discrete Math. 268 (2003), 171-183. MR1983276 (2004b:05006). See Table 1.
FORMULA
G.f.: x*(1 - 9*x + 31*x^2 - 49*x^3 + 37*x^4 - 14*x^5 + 2*x^6) / ((1 - x)*(1 - 3*x + x^2)^2*(1 - 4*x + 2*x^2)).
PROG
(PARI) Vec(x*(1 - 9*x + 31*x^2 - 49*x^3 + 37*x^4 - 14*x^5 + 2*x^6) / ((1 - x)*(1 - 3*x + x^2)^2*(1 - 4*x + 2*x^2)) + O(x^30)) \\ Colin Barker, Oct 23 2017
CROSSREFS
Sequence in context: A165528 A116709 A165529 * A165530 A116707 A116704
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved