In Introduction to Arithmetic, Chapter 16, he says of perfect numbers, "There is a method of producing them, neat and unfailing, which neither passes by any of the perfect numbers nor fails to differentiate any of those that are not such, which is carried out in the following way." He then goes on to explain a procedure which is equivalent to finding a triangular number based on a Mersenne prime.
Zelinsky, Joshua (July 2019). "Upper bounds on the second largest prime factor of an odd perfect number". International Journal of Number Theory. 15 (6): 1183–1189. arXiv:1810.11734. doi:10.1142/S1793042119500659. S2CID62885986..
Kühnel, Ullrich (1950). "Verschärfung der notwendigen Bedingungen für die Existenz von ungeraden vollkommenen Zahlen". Mathematische Zeitschrift (in German). 52: 202–211. doi:10.1007/BF02230691. S2CID120754476.
Konyagin, Sergei; Acquaah, Peter (2012). "On Prime Factors of Odd Perfect Numbers". International Journal of Number Theory. 8 (6): 1537–1540. doi:10.1142/S1793042112500935.
Zelinsky, Joshua (July 2019). "Upper bounds on the second largest prime factor of an odd perfect number". International Journal of Number Theory. 15 (6): 1183–1189. arXiv:1810.11734. doi:10.1142/S1793042119500659. S2CID62885986..
Suryanarayana, D. (1963). "On Odd Perfect Numbers II". Proceedings of the American Mathematical Society. 14 (6): 896–904. doi:10.1090/S0002-9939-1963-0155786-8.
All factors of are congruent to 1 mod 2p. For example, 211 − 1 = 2047 = 23 × 89, and both 23 and 89 yield a remainder of 1 when divided by 22. Furthermore, whenever p is a Sophie Germain prime—that is, 2p + 1 is also prime—and 2p + 1 is congruent to 1 or 7 mod 8, then 2p + 1 will be a factor of which is the case for p = 11, 23, 83, 131, 179, 191, 239, 251, ...OEIS: A002515.
Kühnel, Ullrich (1950). "Verschärfung der notwendigen Bedingungen für die Existenz von ungeraden vollkommenen Zahlen". Mathematische Zeitschrift (in German). 52: 202–211. doi:10.1007/BF02230691. S2CID120754476.
Zelinsky, Joshua (July 2019). "Upper bounds on the second largest prime factor of an odd perfect number". International Journal of Number Theory. 15 (6): 1183–1189. arXiv:1810.11734. doi:10.1142/S1793042119500659. S2CID62885986..