a(n) = n+1 for n <= 2; otherwise a(n) = 3*a(n-3)+1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =7a(5) =10a(6) =13a(7) =22a(8) =31a(9) =40a(10) =67a(11) =94a(12) =121a(13) =202a(14) =283a(15) =364a(16) =607a(17) =850a(18) =1093a(19) =1822a(20) =2551a(21) =3280a(22) =5467a(23) =7654a(24) =9841a(25) =16402a(26) =22963a(27) =29524a(28) =49207a(29) =68890