Trajectory of 3 under map n->21*n+1 if n odd, n->n/2 if n even.

Terms

a(0) =3a(1) =64a(2) =32a(3) =16a(4) =8a(5) =4a(6) =2a(7) =1a(8) =22a(9) =11a(10) =232a(11) =116a(12) =58a(13) =29a(14) =610a(15) =305a(16) =6406a(17) =3203a(18) =67264a(19) =33632a(20) =16816a(21) =8408a(22) =4204a(23) =2102a(24) =1051a(25) =22072a(26) =11036a(27) =5518a(28) =2759a(29) =57940