This is a 5.0-star Fillomino puzzle.
Warning: Untamed specimen ahead.
Well, at least that’s what I think. The first steps are easy; the final steps are scary…but apparently with only 19% cells given, it’s possible to construct a puzzle with a unique solution. Of course it’s possible to construct a 10×10 with 1% cell filled, namely a 100 in that cell, but it’s boring.
And yeah, every given in this puzzle is a prime number. Inspired from a puzzle in mathgrant’s blog…forget which one. 😛