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 A248091 Expansion of x^3*(1-2x-x^2-x^3+x^4+x^5)/((1+x)*(1-3x+x^2-x^3+3x^4)). 1
 0, 0, 0, 1, 0, 1, 1, 3, 6, 16, 39, 101, 259, 670, 1732, 4485, 11613, 30079, 77910, 201812, 522763, 1354153, 3507775, 9086502, 23537592, 60971593, 157940361, 409127579, 1059801190, 2745301576, 7111410031, 18421346973 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,8 COMMENTS a(n) = number of nonisomorphic n-element posets P such that if 1<=i<=n-1, then P has exactly 3 order ideals of cardinality i. REFERENCES R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 1, 2nd ed., 2012, Exercise 3.35c, p. 359. LINKS Index entries for linear recurrences with constant coefficients, signature (2,2,0,-2,-3). MAPLE g := x^3*(x^5+x^4-x^3-x^2-2*x+1)/((x+1)*(3*x^4-x^3+x^2-3*x+1)): gser := series(g, x = 0, 45): seq(coeff(gser, x, n), n = 0 .. 40); MATHEMATICA CoefficientList[Series[x^3*(1 - 2 x - x^2 - x^3 + x^4 + x^5)/((1 + x) (1 - 3 x + x^2 - x^3 + 3 x^4)), {x, 0, 30}], x] (* Wesley Ivan Hurt, Oct 28 2014 *) CROSSREFS Sequence in context: A143560 A279685 A001675 * A168317 A188442 A046211 Adjacent sequences:  A248088 A248089 A248090 * A248092 A248093 A248094 KEYWORD nonn AUTHOR Emeric Deutsch, Oct 28 2014 STATUS approved

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Last modified August 17 05:07 EDT 2022. Contains 356184 sequences. (Running on oeis4.)