A112520 Expansion of 2/(3-sqrt(3-2*sqrt(1-4x))).

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

Offset: 0

Author

Paul Barry, Sep 09 2005

Keywords

• easy
• nonn

Comments

Row sums of number triangle A112519.

Programs

Mathematica

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

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)}}.