[5] De Koninck, J.-M., Luca, F.:
Analytic number theory. Exploring the anatomy of integers. Graduate Studies in Mathematics, vol. 134, American Mathematical Society, Providence, RI, 2012.
MR 2919246
[6] De Koninck, J.-M., Sitaramachandra, R.R.:
Sums involving the largest prime divisor of an integer. Acta Arith. 48 (1987), 3–8.
MR 0893458
[8] Nelson, C., Penny, D.E., Pomerance, C.:
714 and 715. J. Recreational Math. 7 (1974), 87–89.
MR 3821619
[9] Pomerance, C.:
Ruth–Aaron numbers revisited. Paul Erdös and his Mathematics, vol. 11, János Bolyai Math. Soc., Budapest 1999, Bolyai Soc. Math. Stud., 2002, pp. 567–579.
MR 1954715