Number of binary sequences of length n with curling number 2.

Terms

a(0) =0a(1) =2a(2) =2a(3) =6a(4) =12a(5) =26a(6) =52a(7) =110a(8) =214a(9) =438a(10) =876a(11) =1762a(12) =3524a(13) =7084a(14) =14144a(15) =28360a(16) =56720a(17) =113542a(18) =227084a(19) =454448a(20) =908804a(21) =1818168a(22) =3636336a(23) =7273614a(24) =14547228a(25) =29096678a(26) =58192994a(27) =116390424a(28) =232780848a(29) =465569860