Sigma function

This page is about the sigma function that calculates the sume of the factors of a number. To see the page which discusses Rado's sigma function, see busy beaver.

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The sigma function, not to be confused with summation, is the fuction that finds the sum of the positive divisors of a number. The sigma function is denoted by σ(n). If p is a prime number, σ(p) is p+1 because, by definition, the factors of a prime number are 1 and itself.