1. Daniel Shanks and John W. Wrench Jr., “Brun’s Constant,” Math. Comp. 28 (1974) pp. 293–299.
2. G. H. Hardy and J. E. Littlewood, “Some Problems of ‘Partitio Numerorum’ III: On the Expression of a Number as a Sum of Primes,” Acta Math. 44 (1922) pp. 1–70 = G. H. Hardy, Coll. Papers, vol. 1, pp. 561–630.
3. F. J. Gruenberger and G. Armerding, Statistics on the First Six Million Prime Numbers, Reviewed in Math. Comp. 19 (1965) pp. 503–505.
4. Hans Riesel and Robert. C. Vaughan, “On Sums of Primes,” Arkiv für Mat. 21 (1983) pp. 45–74.
5. G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, Fifth edition, Oxford, 1979, p. 351.