4^a(n) is smallest power of 4 beginning with n.

Terms

a(0) =0a(1) =4a(2) =39a(3) =1a(4) =51a(5) =3a(6) =23a(7) =53a(8) =78a(9) =5a(10) =25a(11) =40a(12) =60a(13) =75a(14) =90a(15) =2a(16) =17a(17) =27a(18) =42a(19) =52a(20) =62a(21) =72a(22) =82a(23) =92a(24) =4a(25) =9a(26) =19a(27) =24a(28) =34a(29) =39