1807

This number is a composite.

+ 1807 = 13 × 139 -> 131807139 = 3 × 43935713 -> 313180713943935713 = 8701193 × 35992847641 -> 870119331318071394393571335992847641 = 4872702848504903 × 178570160826665452447 -> 4872702848504903870119331318071394393571335992847641178570160826665452447 = 74923 × 65036141752264376361322041536929839883231264002344289184498229204189. Note that each new semiprime begins and ends with the ordered factors of the previous one. Can you find a larger chain? See PC14. [Sariyar]

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