OFFSET
0,2
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
László Németh and László Szalay, Sequences Involving Square Zig-Zag Shapes, J. Int. Seq., Vol. 24 (2021), Article 21.5.2.
Index entries for linear recurrences with constant coefficients, signature (6,-9,2).
FORMULA
G.f.: 1/((1-2*x)*(1-4*x+x^2)).
a(n) = 6*a(n-1) - 9*a(n-2) + 2*a(n-3), a(0) = 1, a(1) = 6, a(2) = 27.
3*a(n) = -2^(n+2) + A001075(n+2). - R. J. Mathar, Mar 29 2013
a(n) = (-2^(3+n) + (7-4*sqrt(3))*(2-sqrt(3))^n + (2+sqrt(3))^n*(7+4*sqrt(3))) / 6. - Colin Barker, Feb 05 2017
MATHEMATICA
CoefficientList[Series[1/((1 - 2 x)*(1 - 4 x + x^2)), {x, 0, 26}], x] (* Michael De Vlieger, Aug 05 2021 *)
PROG
(PARI) Vec(1/((1-2*x)*(1-4*x+x^2)) + O(x^30)) \\ Colin Barker, Feb 05 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Philippe Deléham, Mar 15 2013
STATUS
approved