A065495 - OEIS

%I #12 Mar 12 2024 07:59:47

%S 1,2,6,14,32,72,156,336,712,1496,3120,6464,13328,27360,55968,114144,

%T 232192,471296,954816,1931264,3900800,7869312,15858432,31928832,

%U 64232704,129128960,259431936,520941056,1045557248,2097616896

%N 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.

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,2,-2,-4).

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

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

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

%K nonn,easy

%O 2,2

%A _Len Smiley_, Nov 24 2001