In number theory, a number used to satisfy the following congruency.
a^phi(b) mod b = a
Where a and b are arbitrary integers.
Phi is calculated by generating the prime power decomposition
of b, then applying the algorithm p^n = p^n-1*p-1 for each base in b.
The prime power decomposition of 100 is:
phi(100) is therefore:
Developed by Euler
as a generalization of Fermat
's little theorem, a^phi(b) mod b is very useful in public key cryptography