A065506 Number of (binary) bit strings of length n having an even length block of 0's followed by an odd length block of 1's.

1, 2, 7, 15, 39, 84, 196, 419, 928, 1965, 4227, 8871, 18742, 39032, 81481, 168606, 349011, 718371, 1477783, 3028412, 6200296, 12660171, 25823604, 52569417, 106908199, 217086287, 440402878, 892384788, 1806730377, 3654428154

Offset: 3

Author

Len Smiley, Nov 26 2001

Keywords

• nonn
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (2,3,-5,-2).

Crossrefs

Cf. A065455.

Formula

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

a(n) = 2^n - A065455(n).