### 2.6.7 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]]`