Number of ternary strings of length n that contain at least two 0's and at most two 1's.

Terms

a(0) =0a(1) =0a(2) =1a(3) =7a(4) =33a(5) =121a(6) =378a(7) =1065a(8) =2803a(9) =7045a(10) =17148a(11) =40789a(12) =95373a(13) =220065a(14) =502414a(15) =1136977a(16) =2553831a(17) =5699149a(18) =12645504a(19) =27914877a(20) =61337665a(21) =134213065a(22) =292547346a(23) =635430937a(24) =1375724763a(25) =2969559381a(26) =6392110468a(27) =13723752805a(28) =29393671413a(29) =62813884465