1. L. M. Adleman, C. Pomerance and R. S. Rumely, On distinguishing prime numbers from composite numbers, Ann. of Math. 117(1983), 173–206.
2. A. Aigner, Das quadratfreie Kern der Eulerschen ϕ-Funktion, Monatsh. Math. 83(1977), 89–91.
3. L. Alaoglu and P. Erdös, A conjecture in elementary number theory, Bull. Amer. Math. Soc. 50(1944), no. 12, 881–882.
4. H. L. Alder, A generalization of Euler’s ϕ-function, Amer. Math. Monthly 65(1958), 690–692.
5. K. Alladi, On arithmetic functions and divisors of higher order, pp. 1–20, in: K. Alladi, New Concepts in Arithmetic Functions, Math.-Science Report 83, The Institute of Math. Sciences, Madras.