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A065495 Number of (binary) bit strings of length n in which an odd length block of 0's is followed by an odd length block of 1's. 3
1, 2, 6, 14, 32, 72, 156, 336, 712, 1496, 3120, 6464, 13328, 27360, 55968, 114144, 232192, 471296, 954816, 1931264, 3900800, 7869312, 15858432, 31928832, 64232704, 129128960, 259431936, 520941056, 1045557248, 2097616896 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

LINKS

Table of n, a(n) for n=2..31.

Index entries for linear recurrences with constant coefficients, signature (2,2,-2,-4).

FORMULA

G.f.: x^2/[(1-2x)(1-2x^2-2x^3)]

EXAMPLE

a(4)=6 because of 0100,0101,1010,1101,0111,0001

CROSSREFS

Cf. A061279 [=2^n - a(n)], A065455, A065494, A065497.

Sequence in context: A232434 A096238 A074878 * A131352 A232230 A294780

Adjacent sequences: A065492 A065493 A065494 * A065496 A065497 A065498

KEYWORD

nonn,easy

AUTHOR

Len Smiley, Nov 24 2001

STATUS

approved

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Last modified January 27 21:49 EST 2023. Contains 359849 sequences. (Running on oeis4.)