Number of ternary sequences which contain 000.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =5a(5) =21a(6) =81a(7) =295a(8) =1037a(9) =3555a(10) =11961a(11) =39667a(12) =130049a(13) =422403a(14) =1361385a(15) =4359115a(16) =13880129a(17) =43984227a(18) =138795849a(19) =436367131a(20) =1367434577a(21) =4272615603a(22) =13315096089a(23) =41397076939a(24) =128429930465a(25) =397665266595