Take sum of squares of digits of previous term; start with 3.

Terms

a(0) =3a(1) =9a(2) =81a(3) =65a(4) =61a(5) =37a(6) =58a(7) =89a(8) =145a(9) =42a(10) =20a(11) =4a(12) =16a(13) =37a(14) =58a(15) =89a(16) =145a(17) =42a(18) =20a(19) =4a(20) =16a(21) =37a(22) =58a(23) =89a(24) =145a(25) =42a(26) =20a(27) =4a(28) =16a(29) =37