The Collaborative International Dictionary
Pythagoreanism \Pyth`a*go"re*an*ism\, n. The doctrines of Pythagoras or the Pythagoreans.
As a philosophic school Pythagoreanism became extinct
in Greece about the middle of the 4th century [B. C.].
--Encyc. Brit.
Wikipedia
Pythagoreanism originated in the 6th century BCE, based on the teachings and beliefs held by Pythagoras and his followers, the Pythagoreans, who were considerably influenced by mathematics and mysticism. Later revivals of Pythagorean doctrines led to what is now called Neopythagoreanism or Neoplatonism. Pythagorean ideas exercised a marked influence on Aristotle, and Plato, and through them, all of Western philosophy.
Historians from the Stanford Encyclopedia of Philosophy pointed out
Usage examples of "pythagoreanism".
The Neopythagorean cult practiced in Rome had departed from true Pythagoreanism, but the preoccupation with numbers and a way of life was still strong.