Fermat sió tēng-lí (Eng-gí: Fermat's little theorem) sī sò͘-lūn lāi-té ê tēng-lí, Iû Hoat-kok sò͘-ha̍k-ka Pierre de Fermat tī 1636 nî hoat-hiān.
Ká-sū x ≡ y ( mod p ) {\displaystyle x\equiv y{\pmod {p}}} , ì-sù sī " x {\displaystyle x} kap y {\displaystyle y} hō͘ p {\displaystyle p} tû ê sî, lóng-ū kâng-khóan ê û-sò͘ (餘數)", jī-chiáⁿ a {\displaystyle a} sī chèng-chéng-sò͘, p {\displaystyle p} sī chit-sò͘, án-ne a p ≡ a ( mod p ) {\displaystyle a^{p}\equiv a{\pmod {p}}} , mā piáu-sī a p − a {\displaystyle a^{p}-a} sī p {\displaystyle p} ê pōe-sò͘.
