Coming to concepts of prime factorization
any number can be expressed as powers of products of prime numbers ,
also the thing to note is that, the number of divisors of a number thus can be obtained by this prime factorization, which is product of (powers+1)
so no of divisor =( a+1)(b+1)....
p has r divisor
28=(a+2)(b+1)k. where k is contribution from other primes than 2 and 3
by trial and error
so 3p has (a+2)(b+2)k divisor