OFFSET
0,2
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
J. Choi, N. Pippenger, Counting the Angels and Devils in Escher's Circle Limit IV, arXiv preprint arXiv:1310.1357, 2013
Index entries for linear recurrences with constant coefficients, signature (4,-1).
FORMULA
a(n) = 8*A001353(n), n>0. - R. J. Mathar, Jan 21 2014
From Colin Barker, Oct 12 2015: (Start)
a(n) = 4*a(n-1)-a(n-2) for n>2.
a(n) = 4*(-(2-sqrt(3))^n+(2+sqrt(3))^n)/sqrt(3) for n>1.
(End)
MATHEMATICA
CoefficientList[Series[(1+4x+x^2)/(1-4x+x^2), {x, 0, 30}], x] (* or *) LinearRecurrence[{4, -1}, {1, 8, 32}, 30] (* Harvey P. Dale, Jul 12 2015 *)
PROG
(PARI) Vec((1+4*x+x^2)/(1-4*x+x^2) + O(x^40)) \\ Colin Barker, Oct 12 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Dec 24 2013
STATUS
approved