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 A198802 Number of closed paths of length n whose steps are 18th roots of unity, U_18(n). 1
 1, 0, 18, 36, 918, 5400, 82800, 801360, 10907190, 132053040, 1802041668, 24199809480, 340640607384, 4834708246368, 70229958125184, 1032223723667136, 15391538570569590, 231935110984687968, 3531542904056225916, 54244559313713885688, 839979883121036697468 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS U_18(n), comment in article: For each m >= 1, the sequence (U_m(N)), N >= 0 is P-recursive but is not algebraic when m > 2. LINKS Andrew Howroyd, Table of n, a(n) for n = 0..200 Gilbert Labelle and Annie Lacasse, Closed paths whose steps are roots of unity, in FPSAC 2011, Reykjavik, Iceland DMTCS proc. AO, 2011, 599-610. FORMULA E.g.f.: g(x)^3 where g(x) is the e.g.f. of A002898. PROG (PARI) seq(n)={Vec(serlaplace(sum(k=0, n, if(k, 2, 1)*(x^k*besseli(k, 2*x + O(x^(n-k+1)))/k!)^3)^3))} \\ Andrew Howroyd, Nov 01 2018 CROSSREFS Cf. A002898, A198808. Sequence in context: A347889 A115550 A061713 * A041638 A041636 A212428 Adjacent sequences: A198799 A198800 A198801 * A198803 A198804 A198805 KEYWORD nonn AUTHOR Simon Plouffe, Oct 30 2011 STATUS approved

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Last modified September 24 19:02 EDT 2023. Contains 365581 sequences. (Running on oeis4.)