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 A001925 From rook polynomials. (Formerly M4151 N1724) 4
 1, 6, 22, 64, 162, 374, 809, 1668, 3316, 6408, 12108, 22468, 41081, 74202, 132666, 235160, 413790, 723530, 1258225, 2177640, 3753096, 6444336, 11028792, 18818664, 32024977, 54367374, 92094334, 155688208, 262711866, 442556798, 744355673, 1250157228 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 REFERENCES J. Riordan, Discordant permutations, Scripta Math., 20 (1954), 14-23. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS T. D. Noe, Table of n, a(n) for n = 0..1000 Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992. Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992. J. Riordan, Discordant permutations, Scripta Math., 20 (1954), 14-23. [Annotated scanned copy] FORMULA Riordan gives the g.f. (1+x)/[(1-x-x^2)^2*(1-x)^3]. MAPLE A001925:=-(1+z)/(z**2+z-1)**2/(z-1)**3; [Conjectured by Simon Plouffe in his 1992 dissertation.] MATHEMATICA nn = 40; CoefficientList[Series[(1 + x)/((1 - x - x^2)^2*(1 - x)^3), {x, 0, nn}], x] (* T. D. Noe, Aug 17 2012 *) CROSSREFS Cf. A002940. Sequence in context: A053739 A280481 A055797 * A002663 A099855 A003469 Adjacent sequences:  A001922 A001923 A001924 * A001926 A001927 A001928 KEYWORD nonn AUTHOR STATUS approved

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Last modified February 22 20:16 EST 2019. Contains 320404 sequences. (Running on oeis4.)