OFFSET
0,4
LINKS
Robert Israel, Table of n, a(n) for n = 0..2991
Index entries for linear recurrences with constant coefficients, signature (0,2,4).
FORMULA
a(n) = (6*2^n - (3+i)*(-1+i)^n - (3-i)*(-1-i)^n)/20. - Ivan Neretin, May 27 2015
G.f.: (x^2+x)/(1-2*x^2-4*x^3). - Robert Israel, May 27 2015
MAPLE
f:= gfun:-rectoproc({a(n)=2*a(n-2)+4*a(n-3), a(0)=0, a(1)=1, a(2)=1}, a(n), remember):
seq(f(n), n=0..100); # Robert Israel, May 27 2015
MATHEMATICA
Nest[Append[#, 2 #[[-2]] + 4 #[[-3]]] &, {0, 1, 1}, 15] (* Ivan Neretin, May 27 2015 *)
CoefficientList[Series[x (1 + x)/((1 - 2 x) (2 x^2 + 2 x + 1)), {x, 0, 40}], x] (* Vincenzo Librandi, May 28 2015 *)
PROG
(Magma) [n le 3 select Floor(n/2) else 2*Self(n-2)+4*Self(n-3): n in [1..40]]; // Vincenzo Librandi, May 28 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paul Curtz, Jan 29 2008
EXTENSIONS
More terms from Robert Israel, May 27 2015
STATUS
approved