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A288668
a(n) = a(n-2) + 2*a(n-3) for n >= 3, where a(0) = 2, a(2) = 4, a(3) = 5.
2
2, 4, 5, 8, 13, 18, 29, 44, 65, 102, 153, 232, 357, 538, 821, 1252, 1897, 2894, 4401, 6688, 10189, 15490, 23565, 35868, 54545, 82998, 126281, 192088, 292277, 444650, 676453, 1029204, 1565753, 2382110, 3624161, 5513616, 8388381, 12761938, 19415613, 29538700
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->0110, 10->000, starting with 00; see A288665.
FORMULA
a(n) = a(n-2) + 2*a(n-3) for n >= 3, where a(0) = 2, a(2) = 4, a(3) = 5.
G.f.: (-2 - 4*x - 3*x^2)/(-1 + x^2 + 2*x^3).
MATHEMATICA
LinearRecurrence[{0, 1, 2}, {2, 4, 5}, 40]
CROSSREFS
Cf. A288665.
Sequence in context: A164571 A238589 A327045 * A377123 A264800 A293189
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 15 2017
STATUS
approved