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 A226433 The number of permutations of length n in a particular geometric grid class. 2
 1, 2, 6, 19, 56, 157, 428, 1149, 3058, 8097, 21370, 56279, 147990, 388727, 1020252, 2676139, 7016372, 18389377, 48184544, 126229809, 330635974, 865940277, 2267709166, 5938235819, 15549095466, 40713244907, 106599027888, 279100615999, 730736374568, 1913175616597 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This geometric grid class is given by the array [[0,1,0],[0,0,*],[1,-1,0]]. A picture is given in the LINKS section. LINKS Jay Pantone, The Enumeration of Permutations Avoiding 3124 and 4312, arXiv:1309.0832 [math.CO], (2013) Jay Pantone, Picture of the geometric grid class Index entries for linear recurrences with constant coefficients, signature (7,-18,21,-11,2) FORMULA G.f.: x*(1-5*x+10*x^2-8*x^3+x^5)/((1-x)^2*(1-2*x)*(1-3*x+x^2)). a(n) = 2*A001519(n)-2^(n-2)-n+1, n>1. - R. J. Mathar, Aug 31 2013 PROG (PARI) x='x+O('x^66); Vec((x-5*x^2+10*x^3-8*x^4+x^6)/((1-x)^2*(1-2*x)*(1-3*x+x^2))) \\ Joerg Arndt, Jun 19 2013 CROSSREFS Sequence in context: A027098 A183305 A192715 * A121483 A077834 A067675 Adjacent sequences:  A226430 A226431 A226432 * A226434 A226435 A226436 KEYWORD nonn AUTHOR Jay Pantone, Jun 06 2013 STATUS approved

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Last modified August 16 23:58 EDT 2018. Contains 313809 sequences. (Running on oeis4.)