Significance: a(n+1)-1 is the count of numbers < primorial(n+1) whose largest prime divisor is <= prime(n). E.g., a(5) = 39 is the index of 210=2*3*5*7 in A090958, which means there are 38 numbers of the form 2^a*3^b*5^c < 210. Can someone derive a general formula (asymptotic)?