A. Granville, INTEGERS, WITHOUT LARGE PRIME FACTORS, IN ARITHMETIC PROGRESSIONS .2., Philosophical transactions-Royal Society of London. Physical sciences and engineering, 345(1676), 1993, pp. 349-362
We show that, for any fixed epsilon > 0, there are asymptotically the
same number of integers up to x, that are composed only of primes less
-than-or-equal-to y, in each arithmetic progression (mod q), provided
that y greater-than-or-equal-to q1+epsilon and log x/log q --> infinit
y as y --> infinity : this improves on previous estimates.