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A287439
a(n) = 2*a(n-2) + 2*a(n-3) for n >= 3, where a(0) = 2, a(2) = 4, a(3) = 7.
3
2, 4, 7, 12, 22, 38, 68, 120, 212, 376, 664, 1176, 2080, 3680, 6512, 11520, 20384, 36064, 63808, 112896, 199744, 353408, 625280, 1106304, 1957376, 3463168, 6127360, 10841088, 19181056, 33936896, 60044288, 106235904, 187962368, 332560384, 588396544
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->000, starting with 00; see A288729.
FORMULA
a(n) = 2*a(n-2) + 2*a(n-3) for n >= 3, where a(0) = 2, a(2) = 4, a(3) = 7.
G.f.: (-2 - 4*x - 3*x^2)/(-1 + 2*x^2 + 2*x^3).
MATHEMATICA
LinearRecurrence[{0, 2, 2}, {2, 4, 7}, 40]
CROSSREFS
Cf. A287372.
Sequence in context: A289107 A221944 A257932 * A026713 A288996 A289153
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 17 2017
STATUS
approved