A116733 - OEIS

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A116733

Number of permutations of length n which avoid the patterns 321, 1324, 2341.

0

1, 2, 5, 12, 24, 41, 63, 90, 122, 159, 201, 248, 300, 357, 419, 486, 558, 635, 717, 804, 896, 993, 1095, 1202, 1314, 1431, 1553, 1680, 1812, 1949, 2091, 2238, 2390, 2547, 2709, 2876, 3048, 3225, 3407, 3594, 3786, 3983, 4185, 4392, 4604, 4821, 5043, 5270

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..48.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

G.f.: -x*(x^4+2*x^3+2*x^2-x+1)/(x-1)^3.

For n >= 3, a(n) = (5*n^2 - 21*n + 28)/2. - Franklin T. Adams-Watters, Sep 16 2006

CROSSREFS

Sequence in context: A379836 A112287 A127787 * A116721 A294868 A192981

Adjacent sequences: A116730 A116731 A116732 * A116734 A116735 A116736

KEYWORD

nonn,easy

AUTHOR

Lara Pudwell, Feb 26 2006

STATUS

approved