Double Mersenne number
In mathematics, a double Mersenne number is a Mersenne number of the form M M p = 2 2 p − 1 − 1 {\displaystyle M_{M_{p}}=2^{2^{p}-1}-1} where p {\displaystyle p} is prime. == Examples == The first four terms of the sequence of double Mersenne numbers are (sequence A077586 in the OEIS): M M 2 = M 3 = 7 {\displaystyle M_{M_{2}}=M_{3}=7} M M 3 = M 7 = 127 {\displaystyle M_{M_{3}}=M_{7}=127} M M 5 = M 31 = 2147483647 {\displaystyle M_{M_{5}}=M_{31}=2147483647} M M 7 = M 127 = 170141183460469231731687303715884105727 {\displaystyle M_{M_{7}}=M_{127}=170141183460469231731687303715884105727} == Double Mersenne primes == A double Mersenne number that is prime is called a double Mersenne prime.