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A055389 a(0)=1, then twice the Fibonacci sequence. 13
1, 2, 2, 4, 6, 10, 16, 26, 42, 68, 110, 178, 288, 466, 754, 1220, 1974, 3194, 5168, 8362, 13530, 21892, 35422, 57314, 92736, 150050, 242786, 392836, 635622, 1028458, 1664080, 2692538, 4356618, 7049156, 11405774, 18454930, 29860704, 48315634, 78176338 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(n) is the number of sequences over the alphabet {0,1} such that all maximal blocks (of both 0's and 1's) have odd length. - Geoffrey Critzer, Mar 06 2012

LINKS

Table of n, a(n) for n=0..38.

Index entries for linear recurrences with constant coefficients, signature (1,1).

FORMULA

G.f.: (1+x-x^2)/(1-x-x^2).

EXAMPLE

a(4) = 6 because we have 0001, 0101, 0111, 1000, 1010, 1110. - Geoffrey Critzer, Mar 06 2012

MATHEMATICA

Join[{1}, Table[2*Fibonacci[n], {n, 70}]] (* Vladimir Joseph Stephan Orlovsky, Feb 10 2012 *)

PROG

(PARI) a(n)=if(n, 2*fibonacci(n), 1) \\ Charles R Greathouse IV, Oct 03 2016

CROSSREFS

Essentially the same as A006355.

Sequence in context: A006355 * A163733 A198834 A270925 A084202 A053637

Adjacent sequences:  A055386 A055387 A055388 * A055390 A055391 A055392

KEYWORD

easy,nonn

AUTHOR

Robert G. Wilson v, Jul 05 2000

EXTENSIONS

More terms from James A. Sellers, Jul 07 2000

STATUS

approved

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Last modified August 19 01:40 EDT 2017. Contains 290789 sequences.