Let a1, a2, ..., an be positivereal numbers, and for k = 1, 2, ..., n define the averages Sk as follows:
The numerator of this fraction is the elementary symmetric polynomial of degree k in the n variables a1, a2, ..., an, that is, the sum of all products of k of the numbers a1, a2, ..., an with the indices in increasing order. The denominator is the number of terms in the numerator, the binomial coefficient
Maclaurin's inequality is the following chain of inequalities:
with equality if and only if all the ai are equal.
For n = 2, this gives the usual inequality of arithmetic and geometric means of two numbers. Maclaurin's inequality is well illustrated by the case n = 4: