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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
OFFSET
1,2
FORMULA
G.f.: A(x) = -{x(x^4+2x^3+2x^2-x+1)}/{(x-1)^3}
For n >= 3, a(n) = (5n^2 - 21n + 28)/2. - Franklin T. Adams-Watters, Sep 16 2006
CROSSREFS
Sequence in context: A326510 A112287 A127787 * A116721 A294868 A192981
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved