The starting point of the present paper are the papers of Schinzel [10] and of Conway, Guy, Schneeberger and Sloane [4]. Following recent papers ([1], [4], [6], [7]) a composite n is called a pseudoprime to base b if bn−1 ≡ 1 mod n. This definition does not coincide with the definition given in my book [9], where I defined (i) a pseudoprime as a composite… (More)