题目
What is the greatest possible value of n such that is divisible by 5n?
解析
\[
(\sqrt{15!} + \sqrt{16!})^2
\]
\[
(\sqrt{15!})^2 + (\sqrt{16!})^2 + 2(\sqrt{15!} \times \sqrt{16!})
\]
\[
15! + 16! + 2(15! \times \sqrt{16})
\]
\[
15! + 16! + 2(15! \times 4)
\]
\[
15!(1 + 16 + 8) = 15! \times 25 = 1 \times 2 \times \dots \times 5 \times \dots \times 10 \times \dots \times 15 \times 25
\]
所以,这个数中包含因子 \(5^5\)。
答案 = 5 ✅