1. T. Agoh, “On Giuga’s conjecture,” Manuscr. Math., 87, No. 4, 501–510 (1995).
2. W. D. Banks, C. W. Nevans, and C. Pomerance, “A remark on Giuga’s conjecture and Lehmer’s totient problem,” Alban. J. Math., 3, No. 2, 81–85 (2009).
3. E. Bedocchi, “Note on a conjecture about prime numbers,” Riv. Mat. Univ. Parma, 11, No. 4, 229–236 (1985).
4. N. G.W. H. Beeger, “On composite numbers n for which a n−1 ≡ (mod n) for every a prime to n,” Scr. Math., 16, 133–135 (1950).
5. D. Borwein, J. M. Borwein, P. B. Borwein, and R. Girgensohn, “Giuga’s conjecture on primality,” Amer. Math. Mon., 103, No. 1, 40–50 (1996).