| − | An '''arithmetic progression''' is a sequence of numbers in which the difference between any number and its predecessor is constant, as in 2, 4, 6, 8, 10. [[Dirichlet's theorem]] states that there are infinitely many [[prime number]]s in any arithmetic progression. | + | An '''arithmetic progression''' is a sequence of numbers in which the difference between any number and its predecessor is constant, as in 2, 4, 6, 8, 10.... |