Ramanujan, Srinivasa (2000), "Question 469", in Hardy, G. H.; Aiyar, P. V. Seshu; Wilson, B. M. (eds.), Collected papers of Srinivasa Ramanujan, Providence, Rhode Island: AMS Chelsea Publishing, p. 327, ISBN0-8218-2076-1, MR2280843
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Ramanujan, Srinivasa (2000), "Question 469", in Hardy, G. H.; Aiyar, P. V. Seshu; Wilson, B. M. (eds.), Collected papers of Srinivasa Ramanujan, Providence, Rhode Island: AMS Chelsea Publishing, p. 327, ISBN0-8218-2076-1, MR2280843
Overholt, Marius (1993), "The Diophantine equation n! + 1 = m2", The Bulletin of the London Mathematical Society, 25 (2): 104, doi:10.1112/blms/25.2.104, MR1204060
Erdős, Paul (1963), "Quelques problèmes de la théorie des nombres"(PDF), in Chabauty, C.; Chatelet, A.; Chatelet, F.; Descombes, R.; Pisot, C.; Poitou, G. (eds.), Introduction à la théorie des nombres, Monographies de l'Enseignement Mathématique (in French), vol. 6, University of Geneva, pp. 81–135; see problème 67, p. 129