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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Conjecture:  a(n) is the number of letters (0s and 1s) in the n-th iterate of the mapping 00->1000, 10->000, starting with 00; see A288729.

LINKS

Clark Kimberling, Table of n, a(n) for n = 0..2000

Index entries for linear recurrences with constant coefficients, signature (0, 2, 2).

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

Adjacent sequences:  A287436 A287437 A287438 * A287440 A287441 A287442

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Jun 17 2017

STATUS

approved

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Last modified July 23 11:44 EDT 2019. Contains 325254 sequences. (Running on oeis4.)