OFFSET
0,3
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
A. Goupil, M.-E. Pellerin and J. de Wouters d'Oplinter, Snake Polyominoes, arXiv preprint arXiv:1307.8432 [math.CO], 2013-2014.
Index entries for linear recurrences with constant coefficients, signature (3,-2,1,-1).
FORMULA
a(n) = 3*a(n-1) - 2*a(n-2) + a(n-3) - a(n-4) for n>3. - Colin Barker, Dec 05 2018
a(n) = 2*a(n-1) + a(n-3) + 2 for n>4. - Greg Dresden, Feb 09 2020
MATHEMATICA
Join[{1, 1}, LinearRecurrence[{3, -2, 1, -1}, {2, 6, 14, 32}, 33]] (* Jean-François Alcover, Dec 05 2018 *)
PROG
(PARI) Vec((1 - 2*x + x^2 + x^3 + x^5) / ((1 - x)*(1 - 2*x - x^3)) + O(x^40)) \\ Colin Barker, Dec 05 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 23 2013
STATUS
approved