Factorial( n )
Factorial
returns the factorial n! of the positive integer n,
which is defined as the product 1 * 2 * 3 * .. * n.
n! is the number of permutations of a set of n elements. 1/n! is the coefficient of x^n in the formal series e^x, which is the generating function for factorial.
gap> List( [0..10], Factorial ); [ 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800 ] gap> Factorial( 30 ); 265252859812191058636308480000000
PermutationsList
(see PermutationsList) computes the set of all
permutations of a list.
GAP 3.4.4