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A116712
Number of permutations of length n which avoid the patterns 231, 3214, 4312.
1
1, 2, 5, 12, 27, 59, 126, 265, 551, 1136, 2327, 4743, 9630, 19493, 39363, 79336, 159659, 320915, 644414, 1293009, 2592783, 5196512, 10410735, 20850127, 41746622, 83568269, 167257931, 334712280, 669742371, 1339998971
OFFSET
1,2
LINKS
Michael Dairyko, Lara Pudwell, Samantha Tyner, Casey Wynn, Non-contiguous pattern avoidance in binary trees. Electron. J. Combin. 19 (2012), no. 3, Paper 22, 21 pp. MR2967227. - From N. J. A. Sloane, Feb 01 2013
FORMULA
G.f.: A(x) = (x^3-x+1)*x/((2*x-1)*(x^2+x-1)).
a(n) = A257113(n+1) - A000045(n+2). - R. J. Mathar, Nov 07 2017
MATHEMATICA
CoefficientList[Series[(x^3-x+1)/((2*x-1)*(x^2+x-1)), {x, 0, 50}], x] (* Stefano Spezia, Nov 29 2018 *)
CROSSREFS
Sequence in context: A129983 A307265 A083378 * A000102 A304175 A086589
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved