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 A172395 G.f. satisfies: A(x) = G(x/A(x)) where o.g.f. G(x) = A(x*G(x)) = Sum_{n>=0} A000085(n)*x^n. 1
 1, 1, 1, 0, 1, 0, 4, 0, 27, 0, 248, 0, 2830, 0, 38232, 0, 593859, 0, 10401712, 0, 202601898, 0, 4342263000, 0, 101551822350, 0, 2573779506192, 0, 70282204726396, 0, 2057490936366320, 0, 64291032462761955, 0, 2136017303903513184, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 COMMENTS The e.g.f. of A000085 is exp(x+x^2/2) = Sum_{n>=0} A000085(n)*x^n/n!, where A000085(n) is the number of self-inverse permutations on n letters. LINKS Table of n, a(n) for n=0..35. Aoife Hennessy, A Study of Riordan Arrays with Applications to Continued Fractions, Orthogonal Polynomials and Lattice Paths, Ph. D. Thesis, Waterford Institute of Technology, Oct. 2011. FORMULA a(2n-2) = A000699(n), the number of irreducible diagrams with 2n nodes, for n>=1. a(2n-1) = 0 for n>=2, with a(1)=1. EXAMPLE G.f.: A(x) = 1 + x + x^2 + x^4 + 4*x^6 + 27*x^8 + 248*x^10 +... where G(x) = A(x*G(x)) is the o.g.f. of A000085: G(x) = 1 + x + 2*x^2 + 4*x^3 + 10*x^4 + 26*x^5 + 76*x^6 + 232*x^7 +... while the e.g.f. of A000085 is given by: exp(x+x^2/2) = 1 + x + 2*x^2/2! + 4*x^3/3! + 10*x^4/4! + 26*x^5/5! +... PROG (PARI) {a(n)=local(G=sum(m=0, n, m!*polcoeff(exp(x+x^2/2+x*O(x^m)), m)*x^m)+x*O(x^n)); polcoeff(x/serreverse(x*G), n)} CROSSREFS Cf. A000085, A000699, A172394 (variant). Sequence in context: A269276 A359521 A172394 * A358653 A270281 A270728 Adjacent sequences: A172392 A172393 A172394 * A172396 A172397 A172398 KEYWORD nonn AUTHOR Paul D. Hanna, Feb 06 2010 STATUS approved

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Last modified February 26 10:09 EST 2024. Contains 370340 sequences. (Running on oeis4.)