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A112520 Expansion of 2/(3-sqrt(3-2*sqrt(1-4x))). 1
1, 1, 1, 3, 6, 21, 54, 195, 573, 2086, 6646, 24289, 81540, 299136, 1040262, 3832923, 13660698, 50572983, 183450064, 682447378, 2507959846, 9374078232, 34791088014, 130624080993, 488542321116, 1841890385196, 6931198308924 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Row sums of number triangle A112519.

LINKS

Table of n, a(n) for n=0..26.

FORMULA

a(n)=sum{k=0..n, sum{j=0..n, (k/n)(-1)^(j-k)C(2n-j-1, n-j)C(2j-k-1, j-k)}}.

MATHEMATICA

CoefficientList[Series[2/(3-Sqrt[3-2*Sqrt[1-4x]]), {x, 0, 30}], x] (* Harvey P. Dale, Nov 28 2016 *)

CROSSREFS

Sequence in context: A148611 A148612 A098511 * A148613 A148614 A148615

Adjacent sequences:  A112517 A112518 A112519 * A112521 A112522 A112523

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Sep 09 2005

STATUS

approved

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Last modified June 18 20:45 EDT 2021. Contains 345121 sequences. (Running on oeis4.)