# Jordan's totient function

Let be a positive integer. In number theory, Jordan's totient function of a positive integer is the number of -tuples of positive integers all less than or equal to that form a coprime -tuple together with . This is a generalisation of Euler's totient function, which is . The function is named after Camille Jordan.

## Definition

Jordan's totient function is multiplicative and may be evaluated as ## Properties

• which may be written in the language of Dirichlet convolutions as and via Möbius inversion as .

Since the Dirichlet generating function of is and the Dirichlet generating function of is , the series for becomes .
• An average order of is . ,

and by inspection of the definition (recognizing that each factor in the product over the primes is a cyclotomic polynomial of ), the arithmetic functions defined by or can also be shown to be integer-valued multiplicative functions.

• .      

## Order of matrix groups

The general linear group of matrices of order over has order The special linear group of matrices of order over has order The symplectic group of matrices of order over has order The first two formulas were discovered by Jordan.

## Examples

Multiplicative functions defined by ratios are J2(n)/J1(n) in , J3(n)/J1(n) in , J4(n)/J1(n) in , J5(n)/J1(n) in , J6(n)/J1(n) in , J7(n)/J1(n) in , J8(n)/J1(n) in , J9(n)/J1(n) in , J10(n)/J1(n) in , J11(n)/J1(n) in .

Examples of the ratios J2k(n)/Jk(n) are J4(n)/J2(n) in , J6(n)/J3(n) in , and J8(n)/J4(n) in .

## Notes

1. Sándor & Crstici (2004) p.106
2. Holden et al in external links The formula is Gegenbauer's
3. All of these formulas are from Andrici and Priticari in #External links