Cnk is the coefficient of binomial theorem, also known as Newton's binomial theorem, which was put forward by Newton from 1664 to 1665. This theorem gives the integer power of the sum of two numbers.

The formula of the combination number cnk is: cnk = [n (n-1) (n-2) ... (n-k+1)]

The significance of Cnk theorem:

Newton invented calculus based on Cnk theorem, and its application in elementary mathematics mainly lies in some rough analysis and estimation and the proof of identities.

This theorem also has its place in genetics, and its specific application scope is to infer the genotype and probability of inbred offspring, the phenotype and probability of inbred offspring, the phenotype distribution and probability of hybrid offspring, the performance and probability of hybrid inbred offspring obtained through test crossing, the sex distribution and probability of children born to husband and wife, and the gene or genotype frequency of balanced population.