题目
If the prime factorization of the integer q can be expressed as a2xbxc3x−1, where a, b, c, and x are distinct positive integers, which of the following could be the total number of factors of q?
选项
A.3j + 4, where j is a positive integer
B.5k + 5, where k is a positive integer
C.6l + 2, where l is a positive integer
D.9m + 7, where m is a positive integer
E.10n + 1, where n is a positive integer
解析
如果整数\(q\)的质因数分解可以表示为\(a^{2x}b^{x}c^{3x - 1}\),其中\(a\)、\(b\)、\(c\)和\(x\)是不同的正整数,以下哪一个可能是\(q\)的因数总数?
- 根据整数因数个数的计算公式,如果一个数\(N = p_1^{a_1}p_2^{a_2}\cdots p_n^{a_n}\),其因数的个数为\((a_1 + 1)(a_2+1)\cdots(a_n + 1)\)。
- 对于整数\(q=a^{2x}b^{x}c^{3x - 1}\),其因数的个数为\((2x + 1)(x + 1)(3x)\)。
- 对\((2x + 1)(x + 1)(3x)\)展开可得:
\[
\begin{align*}
&(2x+1)(x + 1)(3x)\\
=&(2x^2+2x+x+1)\times(3x)\\
=&(2x^2 + 3x+1)\times(3x)\\
=&6x^3+9x^2 + 3x\\
=&3x(2x^2 + 3x + 1)\\
\end{align*}
\]
- 令\(x = k+ 1\)(\(k\)是正整数),则:
\[
\begin{align*}
&3(k + 1)[2(k + 1)^2+3(k + 1)+1]\\
=&3(k + 1)[2(k^2 + 2k+1)+3k + 3 + 1]\\
=&3(k + 1)(2k^2+4k + 2 + 3k+4)\\
=&3(k + 1)(2k^2 + 7k+6)\\
=&6k^3 + 21k^2+25k+18\\
=&5k+5+(6k^3+21k^2 + 20k + 13)
\end{align*}
\]
- 所以\(q\)的因数个数可以表示为\(5k + 5\)(\(k\)是正整数)的形式
综上,答案是B选项。