PP-T2-20

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20.
For any positive integer n, the length of n is defined as the number of prime factors whose product is n. For example, the length of 75 is 3, since 75 = 3 ?? 5 ?? 5. How many two-digit positive integers have length 6 ?
(A) None (B) One (C) Two (D) Three (E) Four
Ans:C

[小花]

從最小的質數乘6次看看

2*2*2*2*2*2=64 符合
2*2*2*2*2*3=96 符合

在算下去就超過100了

[max999]

謝謝小花