How it works

The next number in the sequence can be found by looking at its index.

If the index is = prime^power then the previous term has to be multiplied by prime or it is unchanged.

1 - 1
2 - 2 (multiply by 2 because two is prime)
6 - 3 (multiply by 3 because 3 is prime)
12 - 4 (4 = 2^2 and two is prime so multiply by 2)
60 - 5 (5 prime so multiply be 5)
60 - 6 (6 is neither prime nor a prime to some power so stays the same)
420 - 7 (x7)
840 - 8 (8=2^3 so multiply by 2)
2520 - 9 (9=3^2 so multiply by 3)