OFFSET
0,1
COMMENTS
Conjecture: a(n) is the number of letters (0's and 1's) in the n-th iteration of the mapping 00->0101, 10->010, starting with 00; see A288520.
LINKS
Clark Kimberling, Table of n, a(n) for n = 0..10000
Index entries for linear recurrences with constant coefficients, signature (1, 1, 1, -2).
FORMULA
a(n) = a(n-1) + a(n-2) + a(n-3) - 2*a(n-4) for n >= 5, where a(0) = 2, a(1) = 4, a(2) = 5, a(3) = 8, a(4) = 11.
G.f.: (2 + 2 x - x^2 - 3 x^3 - 2 x^4)/(1 - x - x^2 - x^3 + 2 x^4).
MATHEMATICA
Join[{2}, LinearRecurrence[{1, 1, 1, -2}, {4, 5, 8, 11}, 40]]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 13 2017
STATUS
approved