Number of ternary strings of length n which contain 01.

Terms

a(0) =0a(1) =0a(2) =1a(3) =6a(4) =26a(5) =99a(6) =352a(7) =1200a(8) =3977a(9) =12918a(10) =41338a(11) =130779a(12) =410048a(13) =1276512a(14) =3950929a(15) =12170598a(16) =37343834a(17) =114209811a(18) =348332320a(19) =1059927312a(20) =3218870105a(21) =9758944470a(22) =29544747706a(23) =89335651851a(24) =269843267456a(25) =814337329344