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A116780

Number of permutations of length n which avoid the patterns 2341, 4123, 4132.

1, 2, 6, 21, 74, 249, 804, 2540, 7977, 25106, 79327, 251328, 797094, 2527977, 8014590, 25401277, 80494292, 255072244, 808301057, 2561517150, 8117640043, 25725562136, 81526606470, 258364283985, 818775016906, 2594754502777

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..26.

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 124.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (7,-19,27,-19,8,-2).

FORMULA

G.f.: A(x) = -{(2x^5-6x^4+10x^3-11x^2+5x-1)x}/{2x^6-8x^5+19x^4-27x^3+19x^2-7x+1}

MATHEMATICA

LinearRecurrence[{7, -19, 27, -19, 8, -2}, {1, 2, 6, 21, 74, 249}, 30] (* Harvey P. Dale, Aug 03 2017 *)

CROSSREFS

Sequence in context: A116752 A294767 A116827 * A116777 A294768 A116793

Adjacent sequences: A116777 A116778 A116779 * A116781 A116782 A116783

KEYWORD

nonn,easy

AUTHOR

Lara Pudwell, Feb 26 2006

STATUS

approved

URL: https://oeis.org/A116780

⇱ A116780 - OEIS