A106469 Expansion of (1 + x^2)*(1 + 2*x)/(1 - x^2).

1, 2, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4

Offset: 0

Author

Paul Barry, May 03 2005

Keywords

• easy
• nonn

Links

• Index entries for linear recurrences with constant coefficients, signature (0,1).

Crossrefs

Row sums of A106468.

Programs

Mathematica

CoefficientList[Series[(1+x^2)(1+2x)/(1-x^2),{x,0,95}],x] (* James C. McMahon, Feb 02 2024 *)

Formula

a(0)=1, a(n)=(2-0^((n-1)/2))(1-(-1)^n)+(2-0^(n/2))(1+(-1)^n)/2, n>1.