<n> denotes the product of all the positive even integers that are less than n (inclusive), then what is the biggest prime factor of <20>+<22>?
oa to follow.
oa to follow.
let's beat GMAT.
<20> + <22> = <20> * (1 + 22) = <20> * 23
23 is largest prime factor, since all of prime factors of <20> are smaller than 20
<20> = 2 * 4 * 6 * 8 * 10 * 12 * 14 * 16 * 18 * 20: prime factors 2, 3, 5, 7
<22> = <20> * 22
