@Vincenzo -- it's simple, really. Both believed the universe could be explained through numbers. Pythagoras is most known for his famed theorum, but he did a heck of a lot more that that. He even started a religion which was dominated by mathematics -- the right formula could explain anything, see?
Nostradamas was similar in his approach. He didn't see himself as a prophet or necessarily a seer, but subscribed to the notion that one could predict the future based on what had happened in the past. Those theories involved how the planets lined up and the application of a lot of math.
The two regarded themselves as scientists and philosophers and both relied heavily on math.
It does seem odd to say that Pythagoras was a forerunner of Nostradamas, but that is how things worked out in hindsight.