a(1) = 1; if a(n) is not divisible by 3, a(n+1) = 4*a(n) + 1, otherwise a(n+1) = a(n)/3.

Terms

a(0) =1a(1) =5a(2) =21a(3) =7a(4) =29a(5) =117a(6) =39a(7) =13a(8) =53a(9) =213a(10) =71a(11) =285a(12) =95a(13) =381a(14) =127a(15) =509a(16) =2037a(17) =679a(18) =2717a(19) =10869a(20) =3623a(21) =14493a(22) =4831a(23) =19325a(24) =77301a(25) =25767a(26) =8589a(27) =2863a(28) =11453a(29) =45813