x2-3x+1
Perron numbers are named after Oskar Perron; the Perron–Frobenius theorem asserts that, for a real square matrix with positive algebraic entries whose largest eigenvalue is greater than one, this eigenvalue is a Perron number. As a closely related case, the Perron number of a graph is defined to be the spectral radius of its adjacency matrix.
Any Pisot number or Salem number is a Perron number, as is the Mahler measure of a monic integer polynomial.
. Peter Borwein . Computational Excursions in Analysis and Number Theory . . 2007 . 0-387-95444-9 . 24.