Upon reading the question, power of primes immediately come to mind,

2, 4, 8, 16, ... works, but we hit the 1e18 constraint pretty quickly, need to include powers of more primes,

One way is to start from cube of a prime, them when this primes constraint hits, we add a link element between the powers of this prime and the next prime, Link element = p*p*q, p is the prime whose constraint we just hit and q is the next prime.

So link between 2's power's and 3's power's would be 12.

Solution: https://mirror.codeforces.com/contest/2218/submission/370051646