PREP PS2-20. 2942-!-item-!-187;#058&003104

wtx2490467 · 发表于 2011-11-20 23:44:34

20. 2942-!-item-!-187;#058&003104
For any positive integer n, the length of n is defined as thenumber 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 havelength 6 ?

(A) None
(B) One
(C) Two
(D) Three
(E) Four

各位同学,这道题我实在不知道咋算,答案是C,请帮帮我,

avalon9527 · 发表于 2011-11-21 00:17:15

222222=64
222223=96
222225=160 (out)
Only two, 64 and 96. Others have more than 2-digit.

PREP PS2-20. 2942-!-item-!-187;#058&003104

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