Pietro Cataldi
![''Due lettioni'', 1613](https://upload.wikimedia.org/wikipedia/commons/5/5e/Cataldi_-_Due_lettioni_date_nella_academia_erigenda_dove_si_mostra_come_si_trovi_la_grandezza_delle_superficie_rettilinee%2C_1613_-_87568.jpg)
Cataldi discovered the sixth and seventh perfect numbers by 1588. His discovery of the 6th, that corresponding to p=17 in the formula Mp=2p-1, exploded a many-times repeated number-theoretical myth that the perfect numbers had units digits that invariably alternated between 6 and 8. (Until Cataldi, 19 authors going back to Nicomachus are reported to have made the claim, with a few more repeating this afterward, according to L.E.Dickson's ''History of the Theory of Numbers''). Cataldi's discovery of the 7th (for p=19) held the record for the largest known prime for almost two centuries, until Leonhard Euler discovered that 231 - 1 was the eighth Mersenne prime. Although Cataldi incorrectly claimed that p=23, 29, 31 and 37 all also generate Mersenne primes (and perfect numbers), his text's clear demonstration shows that he had genuinely established primality through p=19. Provided by Wikipedia
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