Euler totient
Euler's totient function $\phi$ (not to be confused with the Euler phi) is defined for $n=1,2,3,\ldots$ so that $\phi(n)$ equals the number of positive integers less than or equal to $n$ that are relatively prime to $n$.
Graph of $\phi$ to $3500$.
Properties
Sum of totient equals zeta(z-1)/zeta(z) for Re(z) greater than 2
Sum of totient equals z/((1-z) squared)
Product representation of totient
Euler totient is multiplicative
Videos
Euler's Totient Function: what it is and how it works
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Euler's Totient Function | How To Find Totient Of A Number Using Euler's Product Formula
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References
- 1964: Milton Abramowitz and Irene A. Stegun: Handbook of mathematical functions ... (previous) ... (next): $24.3.2 \mathrm{I}.A.$
