104 (one hundred [and] four) is the natural number following 103 and preceding 105.

104 is a refactorable number and a primitive semiperfect number.

The smallest known 4-regular matchstick graph has 104 edges and 52 vertices, where four unit line segments intersect at every vertex.

The second largest sporadic group ${\displaystyle \mathbb {B} }$ has a McKay–Thompson series, representative of a principal modular function is ${\displaystyle T_{2A}(\tau )}$, with constant term ${\displaystyle a(0)=104}$:

The Tits group ${\displaystyle \mathbb {T} }$, which is the only finite simple group to classify as either a non-strict group of Lie type or sporadic group, holds a minimal faithful complex representation in 104 dimensions.