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A026770 T(2n,n), T given by A026769. 2
1, 2, 7, 28, 120, 538, 2493, 11854, 57558, 284392, 1426038, 7241356, 37173304, 192638992, 1006564439, 5297715628, 28061959428, 149491856978, 800425486692, 4305263668514, 23251846197766, 126044501870378, 685569373724964, 3740339567665558, 20463965229643218, 112250484320225118 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Number of lattice paths from (0,0) to (n,n) with steps (0,1), (1,0) and, when below the diagonal, (1,1). - Alois P. Heinz, Sep 14 2016

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..1000

FORMULA

O.g.f.: 1/(1-x*(C(x)+S(x))), where C(x)=(1-sqrt(1-4x))/(2*x) is o.g.f. for A000108 and S(x)=(1-x-sqrt(1-6*x+x^2))/(2*x) is o.g.f. for A006318. - Max Alekseyev, Dec 02 2015

PROG

(PARI) { C = (1-sqrt(1-4*x+O(x^51)))/2/x; S = (1-x-sqrt(1-6*x+x^2 +O(x^51)))/2/x; Vec(1/(1-x*(C+S))) } /* Max Alekseyev, Dec 02 2015 */

CROSSREFS

Cf. A000108, A006318, A026671, A026769, A026781, A104625, A109980.

Sequence in context: A150656 A150657 A150658 * A241371 A010683 A276852

Adjacent sequences:  A026767 A026768 A026769 * A026771 A026772 A026773

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified March 19 13:37 EDT 2019. Contains 321330 sequences. (Running on oeis4.)