Take sum of squares of digits of previous term; start with 6.

Terms

a(0) =6a(1) =36a(2) =45a(3) =41a(4) =17a(5) =50a(6) =25a(7) =29a(8) =85a(9) =89a(10) =145a(11) =42a(12) =20a(13) =4a(14) =16a(15) =37a(16) =58a(17) =89a(18) =145a(19) =42a(20) =20a(21) =4a(22) =16a(23) =37a(24) =58a(25) =89a(26) =145a(27) =42a(28) =20a(29) =4