Number of length n words on {0,1,2} with no four consecutive 0's.

Terms

a(0) =1a(1) =3a(2) =9a(3) =27a(4) =80a(5) =238a(6) =708a(7) =2106a(8) =6264a(9) =18632a(10) =55420a(11) =164844a(12) =490320a(13) =1458432a(14) =4338032a(15) =12903256a(16) =38380080a(17) =114159600a(18) =339561936a(19) =1010009744a(20) =3004222720a(21) =8935908000a(22) =26579404800a(23) =79059090528a(24) =235157252096a(25) =699463310848