

A089165


Partial sums of the central Delannoy numbers (A001850).


4



1, 4, 17, 80, 401, 2084, 11073, 59712, 325441, 1788004, 9885457, 54932176, 306528145, 1716461764, 9640310017, 54282691840, 306337928449, 1732172652868, 9811489710737, 55660919625680, 316204733423121, 1798580947651044
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OFFSET

0,2


COMMENTS

Number of peaks at odd level in all Schroeder paths (i.e., consisting of steps U=(1,1),D=(1,1),H=(2,0) and never going below the xaxis) from (0,0) to (2n+2,0). Example: a(1)=4 because HH,HU*D,U*DH,UHD,U*DU*D,UUDD contain 4 peaks at odd level (indicated by *).
From EvertJan D. Pol (evertjan.pol(AT)philips.com), Oct 25 2005: "Also appears in the context of infinite lattices of unit resistors. The paper by Atkinson and van Steenwijk shows how to calculate the resulting resistance R(n,p) between two nodes in the lattice that are apart by the vector (n,p). The resulting values can be written in the form r+s/Pi, where r and s are rational numbers.
"Here we concentrate on the rational part r. The paper gives values for a single quadrant in the integer plane. Other quadrants can be filled with mirrorimages of the given quadrant. Casual inspection of the values shows that the numbers are most easily analysed by looking at the diagonals (n+k,nk) for n=0,1,2,... and fixed k. The rational part of the values on these diagonals appears to be a polynomial sequence of degree 2k1, apart from the alternating sign.
"Similarly, the absolute value of the rational part of the values on the diagonals (n+k+1,nk) is a polynomial sequence of degree 2k. Assuming these observations to be true, the entire plane of rational values can be constructed from the single sequence R(0,p)! The values off the axes are simply extrapolated from values on and closer to the axes based on the polynomial form of the diagonals, with the proper sign. The sequence R(0,p) begins with 0, 1/2, 24/Pi, 17/224/Pi, 40368/(3Pi) and twice the rational part of this sequence is A089165. The mathematica program given here is copied verbatim from the paper."
The first Mathematica code produces 0, 1, 4  8/Pi, 17  48/Pi, 80  736/(3*Pi), 401  3760/(3*Pi), 2084  98104/(15*Pi), 11073  521696/(15*Pi), 59712  19696256/(105*Pi), 325441  7156768/(7*Pi), 1788004  1769409304/(135*Pi); ... and the integer part gives the sequence.


LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200
D. Atkinson and F. J. van Steenwijk, Infinite Resistive Lattices.


FORMULA

G.f.: 1/((1z)*sqrt(16*z+z^2)).
a(n) = Sum_{j=0..n} Sum_{i=0..2n} binomial(i, j)*binomial(j, ij).  Benoit Cloitre, Oct 23 2004
a(n) = Sum_{k=0..n} C(n+k+1,2k+1)*A000984(k).  Paul Barry, Jun 03 2009
G.f.: d/dx atan(x*A006318(x)).  Vladimir Kruchinin
Recurrence: n*a(n) = (7*n3)*a(n1)  (7*n4)*a(n2) + (n1)*a(n3).  Vaclav Kotesovec, Oct 14 2012
a(n) ~ sqrt(48+34*sqrt(2))*(3+2*sqrt(2))^n/(8*sqrt(Pi*n)).  Vaclav Kotesovec, Oct 14 2012


MAPLE

G:=1/((1z)*sqrt(16*z+z^2)): Gser:=series(G, z=0, 26): seq(coeff(Gser, z, n), n=0..23); # Emeric Deutsch, May 05 2006


MATHEMATICA

alphas[beta_]:=Log[2Cos[beta]+Sqrt[3+Cos[beta]*(Cos[beta]4)]]; Rsqu[n_, p_]:=Simplify[(1/Pi)*Integrate[(1Exp[ Abs[n]*alphas[beta]]*Cos[p*beta])/Sinh[alphas[beta]], {beta, 0, Pi}]]; Table[Expand[2Rsqu[0, k]], {k, 0, 8}] (EvertJan D. Pol)
f[n_] := Sum[ Binomial[i, j] Binomial[j, ij], {i, 0, 2n}, {j, 0, n}]; Table[ f@n, {n, 0, 21}] (* or *)
CoefficientList[ Series[ 1/((1  x)Sqrt[1  6x + x^2]), {x, 0, 21}], x] (* Robert G. Wilson v, May 04 2006 *)


PROG

(PARI) a(n)=sum(i=0, 2*n, sum(j=0, n, binomial(i, j)*binomial(j, ij)))
(PARI) x + O(x^66); Vec(deriv(atan(x*(1x(16*x+x^2)^(1/2))/(2*x)))) \\ Joerg Arndt, Apr 21 2011


CROSSREFS

Cf. A001850, A006318.
Sequence in context: A218134 A110307 A206228 * A056096 A257084 A245377
Adjacent sequences: A089162 A089163 A089164 * A089166 A089167 A089168


KEYWORD

nonn


AUTHOR

Emeric Deutsch, Dec 06 2003


STATUS

approved



