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A116809

Number of permutations of length n which avoid the patterns 1432, 2134, 2143.

1, 2, 6, 21, 76, 273, 971, 3439, 12172, 43098, 152649, 540730, 1915445, 6785029, 24034177, 85134498, 301565746, 1068215101, 3783864272, 13403320805, 47477655647, 168176809999, 595721056436, 2110181402286, 7474749309041

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OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..1810

D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 [math.CO] (2017), Table 2 No 189.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (6,-12,13,-5,1).

FORMULA

G.f.: A(x) = -{(x-1)^4x}/{x^5-5x^4+13x^3-12x^2+6x-1}

MAPLE

f:= gfun:-rectoproc({a(n)-5*a(n+1)+13*a(n+2)-12*a(n+3)+6*a(n+4)-a(n+5), a(0) = 0, a(1) = 1, a(2) = 2, a(3) = 6, a(4) = 21, a(5) = 76}, a(n), remember):

map(f, [$1..30]); # Robert Israel, Jun 02 2016

MATHEMATICA

LinearRecurrence[{6, -12, 13, -5, 1}, {1, 2, 6, 21, 76}, 25] (* Jean-François Alcover, Sep 19 2018 *)

CROSSREFS

Sequence in context: A294817 A294772 A294818 * A116819 A294819 A294820

Adjacent sequences: A116806 A116807 A116808 * A116810 A116811 A116812

KEYWORD

nonn,easy

AUTHOR

Lara Pudwell, Feb 26 2006

STATUS

approved

URL: https://oeis.org/A116809

⇱ A116809 - OEIS