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 A129880 Sequence d_n arising in enumeration of arrays of directed blocks (see Quaintance reference for precise definition). 2
 1, 1, 4, 10, 32, 101, 334, 1129, 3890, 13618, 48275, 172995, 625574, 2279997, 8366553, 30885640, 114620926, 427383918, 1600323161, 6015226752, 22687991095, 85843131701, 325734335544, 1239274254094, 4726359853214, 18065978123065 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Jocelyn Quaintance, Combinatoric Enumeration of Two-Dimensional Proper Arrays, Discrete Math., 307 (2007), 1844-1864. FORMULA See Quaintance reference for generating functions that produce A129872-A129886. G.f.: D(t) satisfies (t^3 + t^2)*D^3 + (t^3 - t^2 - 2*t)*D^2 + (-t^2 - t + 1)*D - t = 0. Michel Marcus, Mar 29 2013 PROG (PARI) listdn(m) = { my(D = t*O(t)); for (n= 1, m, D = (t - (t^3 + t^2)*D^3 - (t^3 - t^2 - 2*t)*D^2)/(1 - t - t^2); ); return(vector(m, i , polcoeff(D, i, t))); } \\ Michel Marcus, Mar 29 2013 CROSSREFS Sequence in context: A001673 A017936 A033297 * A303832 A316103 A137954 Adjacent sequences:  A129877 A129878 A129879 * A129881 A129882 A129883 KEYWORD nonn AUTHOR N. J. A. Sloane, May 26 2007 STATUS approved

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Last modified April 17 09:29 EDT 2021. Contains 343064 sequences. (Running on oeis4.)