In base 10, the Copeland–Erdos constant 0.23571113171923… is obtained by concatenating the digits of the primes 2, 3, 5, … . Copeland and Erdos proved that this constant is normal in base 10, meaning that in the limit the frequency of each digit is
, the frequency of each block of two digits is
, and so on. The sizes of the pie chart slices show the frequencies of single digits for a given approximation. As more primes are used the slices become more nearly equal, reflecting the constant's statistical normality. No proof of normality is known for this number in other bases.