Becomes prime after n iterations of f(x) = sigma(x)-1 (least inverse of A039655).

Terms

a(0) =2a(1) =6a(2) =4a(3) =27a(4) =12a(5) =9a(6) =121a(7) =301a(8) =930a(9) =484a(10) =578a(11) =441a(12) =1273a(13) =468a(14) =4863a(15) =3171a(16) =9216a(17) =8373a(18) =19692a(19) =19416a(20) =25442a(21) =13440a(22) =19230a(23) =16641a(24) =16804a(25) =83161a(26) =100652a(27) =226181a(28) =203400a(29) =133200