An easy method of finding several rather large prime numbers
Euler uses one of his idoneal numbers, 232, to look for large prime numbers. It seems that if a number is of the two forms naa+1 and nxx+yy and n is idoneal, then it is prime. Euler finds 124 values of a, up to 299, that give prime numbers in this form. One example is 232∙2992+1 = 20741033, a prime greater than 20 million!
Original Source Citation
Nova Acta Academiae Scientiarum Imperialis Petropolitanae, Volume 14, pp. 3-10.
Opera Omnia Citation
Series 1, Volume 4, pp.352-359.