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->0001, 1->10, starting with 00; see A288377.
LINKS
Clark Kimberling, Table of n, a(n) for n = 0..2000
Index entries for linear recurrences with constant coefficients, signature (3, -3, 3, -3, 1).
FORMULA
a(n) = 3*a(n-1) - 3*a(n-2) + 3*a(n-3) - 3*a(n-4) + a(n-5) for n >= 1, where a(0) = 2, a(1) = 4, a(2) = 7, a(3) = 11, a(4) = 20.
G.f.: (-2 + 2 x - x^2 + 4 x^3 - 2 x^4)/(-1 + 3 x - 3 x^2 + 3 x^3 - 3 x^4 + x^5).
MATHEMATICA
LinearRecurrence[{3, -3, 3, -3, 1}, {2, 4, 7, 11, 20}, 40]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 10 2017
STATUS
approved