許慎
Xu Shen categorized Chinese characters into 540 sections, under "section headers" ("bùshǒu", now the standard linguistic and lexicographical term for character radicals): these may be entire characters or simplifications thereof, which also serve as components shared by all the characters in that section. The number of section headers, 540, numerologically equals 6 × 9 × 10, the product of the symbolic numbers of Yin and Yang and the number of the Heavenly Stems. The first section header was 一 ("yī" "one; first") and the last was 亥 ("hài", the last character of the Earthly Branches).