Binomial coefficients : binomial comb nCr

comb or nCr or binomial takes as argument two integers n and p.
comb(n,p) or nCr(n,p) or binomial(n,p) returns $\left(\vphantom{^n_p}\right.$ⁿ_p$\left.\vphantom{^n_p}\right)$ = C_n^p.
Input :

comb(5,2)

Output :

10

Remark
binomial (unlike comb, nCr) may have a third real argument, in this case binomial(n,p,a) returns $\left(\vphantom{^n_p}\right.$ⁿ_p$\left.\vphantom{^n_p}\right)$a^p(1 - a)^n-p.