A116762 - OEIS

%I #10 Nov 08 2017 07:22:54

%S 1,2,6,21,73,223,587,1356,2820,5395,9653,16355,26487,41299,62347,

%T 91538,131178,184023,253333,342929,457253,601431,781339,1003672,

%U 1276016,1606923,2005989,2483935,3052691,3725483

%N Number of permutations of length n which avoid the patterns 1234, 1243, 3421.

%H D. Callan, T. Mansour, <a href="http://arxiv.org/abs/1705.00933">Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns</a>, arXiv:1705.00933 (2017), Table 2 No 61.

%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_07">Index entries for linear recurrences with constant coefficients</a>, signature (7,-21,35,-35,21,-7,1).

%F G.f.: A(x) = {x(x^9-4x^8+3x^7+x^6+8x^5-17x^4+14x^3-13x^2+5x-1)}/{(x-1)^7}

%F For n >= 5, a(n) = (27n^5 - 450n^4 + 4045n^3 - 21450n^2 + 62228n - 74880)/120. - Franklin T. Adams-Watters, Sep 16 2006

%K nonn,easy

%O 1,2

%A _Lara Pudwell_, Feb 26 2006