A079514 Second column of triangular array in A079513.

1, 1, 3, 6, 22, 53, 211, 554, 2306, 6362, 27230, 77580, 338444, 986253, 4362627, 12927170, 57788170, 173452334, 781825066, 2370742868, 10757497972, 32892031042, 150073096238, 462030186916, 2117778107732, 6557906929108, 30176799215196, 93909078262808

Offset: 1

Author

N. J. A. Sloane, Jan 22 2003

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000
• D. Merlini, R. Sprugnoli and M. C. Verri, The tennis ball problem, J. Combin. Theory, A 99 (2002), 307-344 (Table A.2).

Programs

Magma

m:=30; R:=PowerSeriesRing(Rationals(), m); Coefficients(R!( 2*(1-Sqrt(1-4*x))/(2+Sqrt(1-4*x)+Sqrt(1+4*x)) )); // G. C. Greubel, Jan 15 2019

Mathematica

Rest[CoefficientList[Series[2*(1-Sqrt[1-4*x])/(2+Sqrt[1-4*x] +Sqrt[1+ 4*x]), {x, 0, 30}], x]] (* G. C. Greubel, Jan 15 2019 *)

PARI

my(x='x+O('x^30)); Vec(2*(1-sqrt(1-4*x))/(2+sqrt(1-4*x) +sqrt(1 +4*x))) \\ G. C. Greubel, Jan 15 2019

Sage

a=(2*(1-sqrt(1-4*x))/(2+sqrt(1-4*x)+sqrt(1+4*x))).series(x, 30).coefficients(x, sparse=False); a[1:] # G. C. Greubel, Jan 15 2019

Formula

G.f.: 2*(1-sqrt(1-4*x))/(2+sqrt(1-4*x)+sqrt(1+4*x)). - Philippe Deléham, Feb 09 2014

Extensions

More terms from Philippe Deléham, Feb 09 2014