Dedekind psi function
In number theory, the Dedekind psi function is the multiplicative function on the positive integers defined by ψ ( n ) = n ∏ p | n ( 1 + 1 p ) , {\displaystyle \psi (n)=n\prod _{p|n}\left(1+{\frac {1}{p}}\right),} where the product is taken over all primes p {\displaystyle p} dividing n . {\displaystyle n.} (By convention, ψ ( 1 ) {\displaystyle \psi (1)} , which is the empty product, has value 1.) The function was introduced by Richard Dedekind in connection with modular functions.