a(n) = largest prime divisor of A138957(n).

Terms

a(0) =1a(1) =3a(2) =41a(3) =617a(4) =823a(5) =643a(6) =9721a(7) =14593a(8) =3803a(9) =14405693a(10) =10939223a(11) =4156374407a(12) =2663693a(13) =5603770631a(19) =769725127