Unhappy numbers which enter the cycle (4, 16, 37, 58, 89, 145, 42, 20) at 20.

Terms

a(0) =20a(1) =24a(2) =204a(3) =224a(4) =240a(5) =242a(6) =402a(7) =420a(8) =422a(9) =1133a(10) =1313a(11) =1331a(12) =2004a(13) =2024a(14) =2040a(15) =2042a(16) =2204a(17) =2240a(18) =2400a(19) =2402a(20) =2420a(21) =3113a(22) =3131a(23) =3311a(24) =4002a(25) =4020a(26) =4022a(27) =4200a(28) =4202a(29) =4220