A reinforcement of some arithmetic theorems, supported by several demonstrations
Euler looks at primes of the form pp+3qq, all of which seem to be of the form 6n+1 (except 3). He suggests (p. 574) that this has a use in Fermat's little theorem.
Original Source Citation
Novi Commentarii academiae scientiarum Petropolitanae, Volume 8, pp. 105-128.
Opera Omnia Citation
Series 1, Volume 2, pp.556-575.