1. E. Chappell, Five-Figure Mathematical Tables, Chambers, London, 1915. (See MTAC, v. 1, 1943–1945, p. 131, Q 4.)
2. Note on an Absolute Constant of Khintchine;Lehmer, D. H.;Amer. Math. Monthly,1939
3. D. Shanks, MTE 164, MTAC, v. 4, 1950, p. 28.
4. Khintchine’s constant;Shanks, Daniel;Amer. Math. Monthly,1959