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题库 / Prep2007E2-DS-21
Is the integer n odd?
(1) n is divisible by 3.
(2) 2n is divisible by twice as many positive integers as n.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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2n is divisible by twice as many positive integers as n.
意思是：2n的因数个数是n的因数个数的两倍
n的质因数的幂分别+1，再相乘 = n有多少个因数
那么2n就应该有 （1+1）倍的n的因数，那就需要n的质因数都不等于2，说明n一定是奇数
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