Extended data
Similar mathematical symbols:
c? Number of combinations
A (or p)? number of permutations
n? Total number of elements
r? Number of elements participating in the selection
! ? Factorial, such as 5! =5×4×3×2× 1= 120, specify 0! = 1
! ! Half factorial (also called double factorial), for example, 7! ! =7×5×3× 1= 105, 10! ! = 10×8×6×4×2=3840
σ addition
References:
Baidu Encyclopedia "Root Number"