Halp with regex

Hey /prog/,
Lets say I have a file with many lines,
each line consists of a very very long random number (string)
Is it possible to write a regular expression to find the longest series of repeated numbers shared by all lines
aka
120123456789948761238746102347106416239847113958719385
217490812741234567890182472103571938547019112413956138756183756183756817356817356
192346112345678978932671658917612746183724681734682173649187245

(I bolded it for readability)

tldr;
how does I finded biggest repeaded series of numbers contained in all lines? (using regex or something one-line'ish)

>>8
The proof is trivial: regular expression matching is known to be possible in O(n) with respect to the input length ( http://swtch.com/~rsc/regexp/regexp1.html ). Because you can't run algorithms with complexity greater than O(n) in O(n), you can't use a regular expression to perform such an algorithm.

>>9
CRUSHING