Combinatorial Functions
Factorial (!) — factorial function (total arrangements of n objects)
Subfactorial — number of derangements of 
objects, leaving none unchanged
FactorialPower — factorial power
Hyperfactorial — hyperfactorial function
Factorial2 (!!) — double factorial
Binomial — binomial coefficients
Multinomial — multinomial coefficients
CatalanNumber — Catalan numbers
PolygonalNumber — triangular and other polygonal numbers
DeBruijnSequence — de Bruijn sequence on a list of elements
StirlingS1, StirlingS2 — Stirling numbers
PartitionsP, PartitionsQ — number of partitions of an integer
BellB — Bell numbers
BellY — Bell polynomial
FrobeniusNumber — Frobenius number for a list
FiniteGroupCount, FiniteAbelianGroupCount — numbers of groups of given order