a(1) = 1, a(n) = largest prime divisor of A057137(n).

Terms

a(0) =1a(1) =3a(2) =41a(3) =617a(4) =823a(5) =643a(6) =9721a(7) =14593a(8) =3803a(9) =3803a(10) =14405693a(11) =10288065751a(12) =116216501a(13) =12079920647a(14) =7552031a(15) =435503a(17) =106377431a(18) =27961a(19) =27961a(20) =205126079a(21) =84225392753a(23) =437274720469a(24) =12792129877