Partial factorisations of a positive integer
Haskell, 56 bytes

_!1=[[]]
i!n=[j:f|j&lt;-[i..n],mod n j&lt;1,f&lt;-j!div n j]
(2!)


(2!)(1338557220::Int) prints in five minutes on my laptop, when compiled with ghc -O3.

Haskell, 62 bytes, but much faster

i!n|i*i&gt;n=[[n]]|0&lt;1=[i:f|mod n i&lt;1,f&lt;-i!div n i]++(i+1)!n
(2!)


(2!)(1338557220::Int) prints in a quarter of a second on my laptop, when compiled with ghc -O3.