Digital couplets are a kind of couplets, in which numbers are cleverly embedded. Numbers and words are complementary to each other. Introducing mathematical calculus into couplets can enlighten people's thinking wisdom and stimulate readers' interest. Especially those ingenious digital couplets are amazing. In ancient times, someone posted a unique number couplet on their doorstep: the first couplet: 2233445, and the second couplet: 6677889. The horizontal link is: 2473. It is a special couplet composed of numbers, and it is a hidden couplet. The first couplet is missing a "one" and the second couplet is missing a "ten". It is "lack of clothes and food" to connect with digital homophones.