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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
OFFSET
2,2
FORMULA
G.f.: x^2/((1-2*x)*(1-2*x^2-2*x^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
KEYWORD
nonn,easy
AUTHOR
Len Smiley, Nov 24 2001
STATUS
approved