OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,4,-4).
FORMULA
a(n) = 5*4^((n-1)/2)-2 (n odd), 2*4^(n/2)-2 (n even).
G.f.: 3*x*(x+1) / ((x-1)*(2*x-1)*(2*x+1)). [Colin Barker, Feb 15 2013]
a(1)=3, a(2)=6, a(3)=18, a(n)=a(n-1)+4*a(n-2)-4*a(n-3). - Harvey P. Dale, May 09 2013
MATHEMATICA
Rest[CoefficientList[Series[3x (x+1)/((x-1)(2x-1)(2x+1)), {x, 0, 40}], x]] (* or *) LinearRecurrence[{1, 4, -4}, {3, 6, 18}, 40] (* Harvey P. Dale, May 09 2013 *)
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Martin Renner, May 02 2006
EXTENSIONS
More terms from Colin Barker, Feb 15 2013
STATUS
approved