521 can represent three meanings:
1. 521 represents "I love you" and "I am willing" because they have similar homophones;
2. 521 represents May 21st, which is designated as the online Valentine's Day for men;
3. 521 represents a natural integer between 520 and 522.
The Origin of Online Valentine's Day on May 21st
The first fixed festival in the virtual network world is set on May 20th and May 21st every year, because the homophonic sounds of "520" and "521" are "I love you", expressing people's beautiful longing for love. But this festival is only fabricated by Chinese netizens and has no actual international effect 520 Best Gift Giving Guide for Couples
According to the different meanings of "0" and "1", 520 is a holiday designed for women, while 521 is a holiday designed for men. Men can confess "520" (I love you) to their wives, girlfriends, or favorite women on May 20th, while women can confess "521" (I am willing, I love you) to their husbands, boyfriends, or desired men on May 21st.
Therefore, the "Internet Valentine's Day" on May 20th and 21st every year has become an auspicious day for couples to register for marriage and hold grand wedding banquets.
Recommended reading: Here is the most comprehensive guide for obtaining marriage certificates for 520 and 521