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.

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

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/((1-2*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

Adjacent sequences: A065492 A065493 A065494 * A065496 A065497 A065498

Keyword

nonn,easy

Author

Len Smiley, Nov 24 2001

Status

approved