1. Andrica, D.: Note on a conjecture in prime number theory. Studia Univ. Babes-Bolyai Math. 31, 44–48 (1986)
2. G. H. Hardy and E. M. Wright, Unsolved Problems Concerning Primes, See §2.8 and Appendix §3 inAn Introduction to the Theory of Numbers, 5th edition, Oxford University Press (1979), pp. 19, 415–416
3. Hausman, M., Shapiro, H.: On practical numbers. Comm. Pure Appl. Math. 37, 705–713 (1984)
4. Margenstern, M.: Théorie, observations et conjectures. J. Number Theory 37, 1–36 (1991)
5. Melfi, G.: On two conjectures about practical numbers. J. Number Theory 56, 205–210 (1996)