yí / gè / zhèng / zhěng / shù / shì / sù / shù / ruò / qiě / wéi / ruò / tā / zhǐ / yǒu / liǎng / gè / zhèng / yīn / shù

一个正整数是素数若且唯若它只有两个正因数。

A positive integer is prime if and only if it has exactly two positive divisors.