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 A003168 Number of blobs with 2n+1 edges. (Formerly M3574) 20
 1, 1, 4, 21, 126, 818, 5594, 39693, 289510, 2157150, 16348960, 125642146, 976789620, 7668465964, 60708178054, 484093913917, 3884724864390, 31348290348086, 254225828706248, 2070856216759478, 16936016649259364 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n) is the number of ways to dissect a convex (2n+2)-gon with non-crossing diagonals so that no (2m+1)-gons (m>0) appear. - Len Smiley a(n) is the number of plane trees with 2n+1 leaves and all non-leaves having an odd number > 1 of children. - Jordan Tirrell, Jun 09 2017 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Seiichi Manyama, Table of n, a(n) for n = 0..1000 (terms 0..100 from T. D. Noe) Thomas H. Bertschinger, Joseph Slote, Olivia Claire Spencer, Samuel Vinitsky, The Mathematics of Origami, Undergrad Thesis, Carleton College (2016). D. Birmajer, J. B. Gil, M. D. Weiner, Colored partitions of a convex polygon by noncrossing diagonals, arXiv preprint arXiv:1503.05242 [math.CO], 2015. L. Carlitz, Enumeration of two-line arrays, Fib. Quart., Vol. 11 Number 2 (1973), 113-130. Frédéric Chapoton and Philippe Nadeau, Combinatorics of the categories of noncrossing partitions, Séminaire Lotharingien de Combinatoire 78B (2017), Article #37. Michael Drmota, Anna de Mier, Marc Noy, Extremal statistics on non-crossing configurations, Discrete Math. 327 (2014), 103--117. MR3192420. See p. 116, B_b(z). - N. J. A. Sloane, May 18 2014 INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 415 Elżbieta Liszewska, Wojciech Młotkowski, Some relatives of the Catalan sequence, arXiv:1907.10725 [math.CO], 2019. 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. R. C. Read, On the enumeration of a class of plane multigraphs, Aequat. Math. 31 (1986) no 1, 47-63. L. Smiley, Even-gon reference FORMULA a(n) = Sum_{k=1..n} binomial(n, k)*binomial(2*n+k, k-1)/n. G.f.: A(x) = Sum_{n>=0} a(n)*x^(2*n+1) satisfies (A-2*A^3)/(1-A^2)=x. - Len Smiley. D-finite with recurrence 4*n*(2*n + 1)*(17*n - 22)*a(n) = (1207*n^3 - 2769*n^2 + 1850*n - 360)*a(n - 1) - 2*(17*n - 5)*(n - 2)*(2*n - 3)*a(n - 2). - Vladeta Jovovic, Jul 16 2004 G.f.: A(x) = 1/(1-G003169(x)) where G003169(x) is the g.f. of A003169. - Paul D. Hanna, Nov 17 2004 a(n) = JacobiP(n-1,1,n+1,3)/n for n > 0. - Mark van Hoeij, Jun 02 2010 a(n) = 1/(2*n+1)*sum((-1)^j*2^(n-j)*binomial(2*n+1,j)*binomial(3*n-j,2*n),j=0..n). - Vladimir Kruchinin, Dec 24 2010 a(n) = upper left term in M^n, M = the production matrix: 1, 1 3, 3, 1 5, 5, 3, 1 7, 7, 5, 3, 1 9, 9, 7, 5, 3, 1 ... . - Gary W. Adamson, Jul 08 2011 a(n) ~ sqrt(14+66/sqrt(17)) * (71+17*sqrt(17))^n / (sqrt(Pi) * n^(3/2) * 2^(4*n+4)). - Vaclav Kotesovec, Jul 01 2015 From Peter Bala, Oct 05 2015: (Start) a(n) = 1/n * Sum_{i = 0..n} 2^(n-i-1)*binomial(2*n,i)* binomial(n,i+1). O.g.f. = 1 + series reversion( x/((1 + 2*x)*(1 + x)^2) ). Logarithmically differentiating the modified g.f. 1 + 4*x + 21*x^2 + 126*x^3 + 818*x^4 + ... gives the o.g.f. for A114496, apart from the initial term. (End) G.f.: A(x) satisfies A = 1 + x*A^3/(1-x*A^2). - Jordan Tirrell, Jun 09 2017 a(n) = A100327(n)/2 for n>=1. - Peter Luschny, Jun 10 2017 EXAMPLE a(2)=4 because we may place exactly one diagonal in 3 ways (forming 2 quadrilaterals), or not place any (leaving 1 hexagon). MAPLE Order := 40; solve(series((A-2*A^3)/(1-A^2), A)=x, A); A003168 := n -> `if`(n=0, 1, A100327(n)/2): seq(A003168(n), n=0..20); # Peter Luschny, Jun 10 2017 MATHEMATICA a = 1; a[n_] = (2^(-n-1)*(3n)!* Hypergeometric2F1[-1-2n, -2n, -3n, -1])/((2n+1)* n!*(2n)!); Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Jul 25 2011, after Vladimir Kruchinin *) PROG (PARI) a(n)=if(n<0, 0, polcoeff(serreverse((x-2*x^3)/(1-x^2)+O(x^(2*n+2))), 2*n+1)) (PARI) {a(n)=local(A=1+x+x*O(x^n)); for(i=1, n, A=(1+x*A)/(1-x*A)^2); sum(k=0, n, polcoeff(A^(n-k), k))} \\ Paul D. Hanna, Nov 17 2004 (Haskell) import Data.List (transpose) a003168 0 = 1 a003168 n = sum (zipWith (*)    (tail \$ a007318_tabl !! n)    ((transpose \$ take (3*n+1) a007318_tabl) !! (2*n+1)))    `div` fromIntegral n -- Reinhard Zumkeller, Oct 27 2013 CROSSREFS Cf. A049124 (no 2m-gons). Cf. A003169, A100327, A114496, A007318. Row sums of A102537, A243662. Sequence in context: A195262 A162480 A275758 * A211249 A185047 A032326 Adjacent sequences:  A003165 A003166 A003167 * A003169 A003170 A003171 KEYWORD nonn,easy,nice AUTHOR STATUS approved

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Last modified July 28 00:54 EDT 2021. Contains 346316 sequences. (Running on oeis4.)