List of prime factors : ifactors

ifactors has an integer (or a list of integers) as parameter.
ifactors decomposes the integer (or the integers of the list) into prime factors, but the result is given as a list (or a list of lists) in which each prime factor is followed by its multiplicity.
Input :

ifactors(90)

Output :

[2,1,3,2,5,1]

Input :

ifactors(-90)

Output :

[-1,1,2,1,3,2,5,1]

Input :

ifactor([36,52])

Output :

[[2,2,3,2],[2,2,13,1]]