#Maple, 17 bytes
Maple, 17 bytes
n->`*`(seq(1..n))
Usage:
> f:=n->`*`(seq(1..n));
> f(0);
1
> f(5);
120
> f(125);
188267717688892609974376770249160085759540364871492425887598231508353156331613598866882932889495923133646405445930057740630161919341380597818883457558547055524326375565007131770880000000000000000000000000000000