OFFSET
0,1
COMMENTS
Conjecture: a(n) is the number of letters (0's and 1's) in the n-th iterate of the mapping 00->1000, 10->001, starting with 00; see A287372.
LINKS
Clark Kimberling, Table of n, a(n) for n = 0..2000
Index entries for linear recurrences with constant coefficients, signature (1, 1, -1, 1, 1).
FORMULA
a(n) = a(n-1) + a(n-2) - a(n-3) +a(n-4) + a(n-5) for n >= 6, where a(0) = 2, a(1) = 4, a(2) = 7, a(3) = 12, a(4) = 19, a(5) = 31.
G.f.: (-2 - 2*x - x^2 - 3*x^3 - 2*x^4 - x^5)/(-1 + x + x^2 - x^3 + x^4 + x^5).
MATHEMATICA
Join[{2}, LinearRecurrence[{1, 1, -1, 1, 1}, {4, 7, 12, 19, 31}, 40]]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 18 2017
STATUS
approved