Salem numbers

Salem constants, sometimes also called Salem numbers, are a set of numbers of which each point of a Pisot number is a limit point from both sides. The Salem constants are algebraic integers >1 in which one or more of the conjugates is on the unit circle with the others inside (Le Lionnais 1983, p. 150). The smallest known Salem number was found by Lehmer as the largest real root of x^10 + x^9 - x^7 - x^6 - x^5 - x^4 - x^3 + x + 1 = 0, which is σ_1 = 1.17628...

Lehmer's Mahler measure problem | Pisot number