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 A110171 Triangle read by rows: T(n,k) (0<=k<=n) is the number of Delannoy paths of length n that start with exactly k (0,1) steps (or, equivalently, with exactly k (1,0) steps). 3
 1, 2, 1, 8, 4, 1, 38, 18, 6, 1, 192, 88, 32, 8, 1, 1002, 450, 170, 50, 10, 1, 5336, 2364, 912, 292, 72, 12, 1, 28814, 12642, 4942, 1666, 462, 98, 14, 1, 157184, 68464, 27008, 9424, 2816, 688, 128, 16, 1, 864146, 374274, 148626, 53154, 16722, 4482, 978, 162, 18, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A Delannoy path of length n is a path from (0,0) to (n,n), consisting of steps E=(1,0), N=(0,1) and D=(1,1). Column k for k>=1 has g.f. z^k*R^(k-1)*g*(1+z*R), where R=1+zR+zR^2=[1-z-sqrt(1-6z+z^2)]/(2z) is the g.f. of the large Schroeder numbers (A006318) and g = 1/sqrt(1-6z+z^2) is the g.f. of the central Delannoy numbers (A001850). sum(k*T(n,k), k=0..n) = A050151(n) (the partial sums of the central Delannoy numbers) = (1/2)*n*R(n), where R(n) = A006318(n) is the n-th large Schroeder number. From Paul Barry, May 07 2009: (Start) Riordan array ((1+x+sqrt(1-6x+x^2))/(2*sqrt(1-6x+x^2)),(1-x-sqrt(1-6x+x^2))/2). Inverse of Riordan array ((1-2x-x^2)/(1-x^2),x(1-x)/(1+x)). (End) LINKS P. Peart and W.-J. Woan, A divisibility property for a subgroup of Riordan matrices, Discrete Applied Mathematics, Vol. 98, Issue 3, Jan 2000, 255-263. Robert A. Sulanke, Objects Counted by the Central Delannoy Numbers, Journal of Integer Sequences, Volume 6, 2003, Article 03.1.5. W.-j. Woan, The Lagrange inversion formula ..., JIS 10 (2007) 07.7.8, example 5. FORMULA T(n,0) = A002003(n) for n>=1. T(n,1) = A050146(n) for n>=1. Row sums are the central Delannoy numbers (A001850). G.f.: (1+z+Q)/(Q(2-t+tz+tQ)), where Q=sqrt(1-6z+z^2). T(n,k) = x^(n-k)*((1+x)/(1-x))^n. - Paul Barry, May 07 2009 T(n,k) = C(n, k)*hypergeometric([k-n, n], [k+1], -1). - Peter Luschny, Sep 17 2014 From Peter Bala, Jun 29 2015: (Start) T(n,k) = Sum_{i = 0..n} binomial(n,i)*binomial(2*n-k-i-1,n-k-i). Matrix product A118384 * A007318^(-1) Riordan array has the form ( x*h'(x)/h(x), h(x) ) with h(x) = ( 1 - x - sqrt(1 - 6*x + x^2) )/2 and so belongs to the hitting time subgroup H of the Riordan group (see Peart and Woan). (End) EXAMPLE T(2,1)=4 because we have NED, NENE, NEEN and NDE. Triangle starts: 1; 2,1; 8,4,1; 38,18,6,1; 192,88,32,8,1; From Paul Barry, May 07 2009: (Start) Production matrix is 2, 1, 4, 2, 1, 6, 2, 2, 1, 8, 2, 2, 2, 1, 10, 2, 2, 2, 2, 1, 12, 2, 2, 2, 2, 2, 1, 14, 2, 2, 2, 2, 2, 2, 1, 16, 2, 2, 2, 2, 2, 2, 2, 1, 18, 2, 2, 2, 2, 2, 2, 2, 2, 1 (End) MAPLE Q:=sqrt(1-6*z+z^2): G:=(1+z+Q)/Q/(2-t+t*z+t*Q): Gser:=simplify(series(G, z=0, 13)): P:=1: for n from 1 to 10 do P[n]:=coeff(Gser, z^n) od: for n from 0 to 10 do seq(coeff(t*P[n], t^k), k=1..n+1) od; # yields sequence in triangular form MATHEMATICA T[n_, n_] = 1; T[n_, k_] := Sum[Binomial[n, i] Binomial[2n-k-i-1, n-k-i], {i, 0, n}]; Table[T[n, k], {n, 0, 9}, {k, 0, n}] (* Jean-François Alcover, Jun 13 2019 *) PROG (Sage) A110171 = lambda n, k : binomial(n, k)*hypergeometric([k-n, n], [k+1], -1) for n in (0..9): [round(A110171(n, k).n(100)) for k in (0..n)] # Peter Luschny, Sep 17 2014 CROSSREFS Cf. A001850, A002003, A050146, A006318, A050151, A118384. Sequence in context: A201641 A110446 A109979 * A104988 A136225 A089460 Adjacent sequences:  A110168 A110169 A110170 * A110172 A110173 A110174 KEYWORD nonn,tabl AUTHOR Emeric Deutsch, Jul 14 2005 STATUS approved

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Last modified October 20 07:33 EDT 2019. Contains 328252 sequences. (Running on oeis4.)