### 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]]`