Chebyshev's theorem is any of several theorems proven by Russian mathematician Pafnuty Chebyshev.
Bertrand's postulate, that for every n there is a prime between n and 2n. Chebyshev's inequality, on the range of standard deviations around the mean, in statistics Chebyshev's sum inequality, about sums and products of decreasing sequences Chebyshev's equioscillation theorem, on the approximation of continuous functions with polynomials The statement that if the function has a limit at infinity, then the limit is 1 (where is the prime-counting function). This result has been superseded by the prime number theorem.