 The summation symbol

means that "d" goes through all the positive divisors of "m", e.g.formula_6 is the greatest common divisor,

formula_7 is Euler's totient function,

formula_8 is the Möbius function, and

formula_9 is the Riemann zeta function.These formulas come from the definition, Euler's formula formula_10 and elementary trigonometric identities.