Sophie Germain prime
The numbers formula_2 form a Cunningham chain of the first kind of length formula_3, while formula_4 forms a Cunningham chain of the second kind. Each of the pairs formula_5 is a pair of twin primes. Each of the primes formula_6 for formula_7 is a Sophie Germain prime and each of the primes formula_6 for formula_9 is a safe prime.