 In 1544 Michael Stifel introduced the concept of the exponent of a number in Arithmetica integra (1544). Thus 8 can be written as \(2^3\) and 25 as \(5^2\). The notion of an exponent immediately suggests the notion of a logarithm as its inverse function: \(\log_b b^a) = a\). Stifel compared the arithmetic sequence: