The number of irreducible representations is usually equal the number of classes. For point group S1 this statement is true for the complex irreducible representations. The number of real-valued irreducible representations is less than the number of classes.
The sum of the squared characters of the neutral symmetry element over all irreducible representations is equal to the total number of symmetry elements
h = ∑ Χi(E) Χi(E)
This statement is true for the complex irreducible representations but not for the real-valued irreducible representations
Reduction formula: The occurence of i-th irreducible representation in an reducible representation is given by the well known formula
ci = 1/h ∑R nR χi(R)irred χ(R)red
This statement is true for the complex irreducible representations. The norm of the two-dimensional real-valued irreducible representations is 2h (instead of h) meaning that the reduction formula has to be modified:
ci(E) = 1/(2h) ∑R nR χi(R)irred χ(R)red = (∑R nR χi(R)irred χ(R)red) / (∑R nR χi(R)irred χi(R)irred)