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 A243675 Number of hypoplactic classes of 3-parking functions of length n. 8
 1, 1, 7, 67, 741, 8909 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS See Novelli-Thibon (2014) for precise definition. This is almost certainly the sequence of small 4-Schroeder numbers as defined by Yang-Jiang (2021). It would be nice to have a proof. Then we could confirm Weiner's conjectured formula, and extend the sequence. Yang & Jiang (2021) give an explicit formula for the small m-Schroeder numbers in Theorems 2.4 and 2.9. - N. J. A. Sloane, Mar 28 2021 REFERENCES Sheng-Liang Yang and Mei-yang Jiang, The m-Schröder paths and m-Schröder numbers, Disc. Math. (2021) Vol. 344, Issue 2, 112209. doi:10.1016/j.disc.2020.112209. See Table 1. LINKS J.-C. Novelli, J.-Y. Thibon, Hopf Algebras of m-permutations,(m+1)-ary trees, and m-parking functions, arXiv preprint arXiv:1403.5962 [math.CO], 2014. See Fig. 23. FORMULA a(n) = Sum_{i=0..n} Sum_{j=0..i} (-2)^(n-i)*binomial(i,j)*binomial(3i+j, n)*binomial(n+1,i)/(n+1) (conjectured). - Michael D. Weiner, May 25 2017 CROSSREFS The sequences listed in Yang-Jiang's Table 1 appear to be A006318, A001003, A027307, A034015, A144097, A243675, A260332, A243676. - N. J. A. Sloane, Mar 28 2021 Apparently, a(n) = A144097/2, apart from the initial term. - N. J. A. Sloane, Mar 28 2021 Sequence in context: A340973 A199756 A038386 * A082578 A291814 A253386 Adjacent sequences: A243672 A243673 A243674 * A243676 A243677 A243678 KEYWORD nonn,more AUTHOR N. J. A. Sloane, Jun 14 2014 EXTENSIONS Added a(0) = 1. - N. J. A. Sloane, Mar 28 2021 STATUS approved

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Last modified March 27 03:58 EDT 2023. Contains 361553 sequences. (Running on oeis4.)