The cofactor is a 252 digit number, which is not so easy to factor. Luckily, this number was also prime. Quadratic sieve algorithm. Class Group method. Elliptic curve algorithm.
Number field sieve.
Dixon's random squares algorithm. Valle's two-thirds algorithm. Seysen's class group algorithm. H.W. Lenstra Jr. Algorithms in Number Theory. The problem of primality testing and factorization are two distinct problems.