a(n) = 3*a(n-1) + a(n-3), a(0) = 1, a(1) = 1, a(2) = 4.

Terms

a(0) =1a(1) =1a(2) =4a(3) =13a(4) =40a(5) =124a(6) =385a(7) =1195a(8) =3709a(9) =11512a(10) =35731a(11) =110902a(12) =344218a(13) =1068385a(14) =3316057a(15) =10292389a(16) =31945552a(17) =99152713a(18) =307750528a(19) =955197136a(20) =2964744121a(21) =9201982891a(22) =28561145809a(23) =88648181548a(24) =275146527535a(25) =854000728414