(Cryptographic) problems solvable in a polynomial number of arithmetic steps
I did not read the paper as well but the abstract seems to say that an exponenial number of bit operations are required.

Chebyshev's work on congruences and its reformulation in the AKS algorithm show that prime generation is in P. Therefore trial division yields non-trivial factors. In that case, for some number N, you can expect a density of primes of 1/ln(N).

Furthermore, you can have a look at Turing's 1937 PhD thesis on the subject.