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%I #13 Apr 01 2019 10:27:13
%S 1,2,6,21,75,248,735,1952,4697,10378,21320,41163,75363,131808,221561,
%T 359742,566561,868514,1299754,1903649,2734539,3859704,5361555,7340060,
%U 9915417,13230986,17456492,22791511,29469251,37760640
%N Number of permutations of length n which avoid the patterns 1234, 2341, 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 [math.CO] (2017), Table 2 No 143.
%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_08">Index entries for linear recurrences with constant coefficients</a>, signature (8,-28,56,-70,56,-28,8,-1).
%F G.f.: A(x) = -{(2x^7-11x^6+16x^5-33x^4+27x^3-18x^2+6x-1)x}/{(x-1)^8}
%F a(n) = (12n^7 - 119n^6 + 651n^5 - 1505n^4 + 693n^3 + 6664n^2 - 11436n + 10080)/5040. - Franklin T. Adams-Watters, Sep 16 2006
%t LinearRecurrence[{8,-28,56,-70,56,-28,8,-1},{1,2,6,21,75,248,735,1952},40] (* _Harvey P. Dale_, Apr 01 2019 *)
%K nonn,easy
%O 1,2
%A _Lara Pudwell_, Feb 26 2006