103 (one hundred [and] three) is the natural number following 102 and preceding 104.

103 is a prime number, and the largest prime factor of ${\displaystyle 6!+1=721=7\cdot 103}$. The previous prime is 101. This makes 103 a twin prime. It is the fifth irregular prime, because it divides the numerator of the Bernoulli number $${\displaystyle B_{24}=-{\frac {236364091}{2730}}=-{\frac {103\cdot 2294797}{2730}}.}$$

The equation ${\displaystyle 64^{3}+94^{3}=103^{3}+1}$ makes 103 part of a "Fermat near miss".

There are 103 different connected series-parallel partial orders on exactly six unlabeled elements.

103 is conjectured to be the smallest number for which repeatedly reversing the digits of its ternary representation, and adding the number to its reversal, does not eventually reach a ternary palindrome.