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 A000163 Series-parallel numbers. (Formerly M1852 N0732) 1
 2, 8, 34, 136, 538, 2080, 7970, 30224, 113874, 426520, 1590338, 5906640, 21866794, 80725280, 297292610, 1092539736, 4007553922, 14675748416, 53663197698, 195962433328, 714734393378, 2603994002280, 9477643739746, 34463730424720 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 REFERENCES J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 142. 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 Sean A. Irvine, Table of n, a(n) for n = 2..500 FORMULA G.f.: 2*(1+S)/(1-S)^3, where S = g.f. for A000084. [Sean A. Irvine, Oct 14 2009] MATHEMATICA n = 25; s = 1/(1 - x) + O[x]^(n + 1); Do[s = s/(1 - x^k)^Coefficient[s, x^k] + O[x]^(n + 1), {k, 2, n}] ; S = s - 1; CoefficientList[2*(1 + S)/(1 - S)^3 + O[x]^n, x] (* Jean-François Alcover, Feb 09 2016 *) CROSSREFS Sequence in context: A204090 A226495 A111643 * A117616 A228655 A192402 Adjacent sequences:  A000160 A000161 A000162 * A000164 A000165 A000166 KEYWORD nonn AUTHOR EXTENSIONS More terms from Sean A. Irvine, Oct 14 2009 STATUS approved

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