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Number of permutations of length n which avoid the patterns 321, 1324, 2341.
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%I #9 Jul 07 2017 06:26:51

%S 1,2,5,12,24,41,63,90,122,159,201,248,300,357,419,486,558,635,717,804,

%T 896,993,1095,1202,1314,1431,1553,1680,1812,1949,2091,2238,2390,2547,

%U 2709,2876,3048,3225,3407,3594,3786,3983,4185,4392,4604,4821,5043,5270

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

%H Lara Pudwell, <a href="http://faculty.valpo.edu/lpudwell/maple/webbook/bookmain.html">Systematic Studies in Pattern Avoidance</a>, 2005.

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F G.f.: A(x) = -{x(x^4+2x^3+2x^2-x+1)}/{(x-1)^3}

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

%K nonn,easy

%O 1,2

%A _Lara Pudwell_, Feb 26 2006