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GMAT, GRE Factors, Primes, Functions and [ Number Properties ] Problem

For every positive even integer n, the function h(n) is defined to be the product of all the even integers from 2 to n, inclusive. If p is the smallest prime factor of h(100) +1, then p is?

A. Between 2 and 20
B. Between 10 and 20
C. Between 20 and 30
D. Between 30 and 40
E. Greater than 40 




h(100)+1=246...100+1=250(123..50)+1=25050!+1

We have two numbers 


h(100)=25050! and h(100)+1=25050!+1 are consecutive integers. 

Two consecutive integers are co-prime, and co-primes don't share any common factor except 1. The same holds true for integers. Both 50 and 51 are consecutive integers, thus only common factor they share is 1.

h(100)=25050! has all prime numbers from 1 to 50 as its factors, according to above h(100)+1=25050!+1 will not have ANY prime factor from 1 to 50. Hence p (>1), the smallest prime factor of h(100)+1 will be more than 50.


E

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