Prime if n=1, composite otherwise.
A Mersenne prime has the form 2n-1. For 2n-1 to be prime, n must also be prime. Perfect numbers have the form 2n-1(2n-1) where 2n-1 is a Mersenne prime, so when a new Mersenne prime is discovered, another perfect number is also found.
neither prime or composite
It is prime
It would be impossible to list them all, since numbers go on forever, but here are some of them: 2 - Prime 3 - Prime 4 - Composite 5 - Prime 6 - Composite 7 - Prime 8 - Composite 9 - Composite 10 - Composite 11 - Prime 12 - Composite 13 - Prime 14 - Composite 15 - Composite 16 - Composite 17 - Prime 18 - Composite 19 - Prime 20 - Composite 21 - Composite 22 - Composite 23 - Prime 24 - Composite 25 - Composite 26 - Composite 27 - Composite 28 - Composite 29 - Prime 30 - Composite 31 - Prime 32 - Composite 33 - Composite 34 - Composite 35 - Composite 36 - Composite 37 - Prime 38 - Composite 39 - Composite 40 - Composite 41 - Prime 42 - Composite 43 - Prime 44 - Composite 45 - Composite 46 - Composite 47 - Prime 48 - Composite 49 - Composite 50 - Composite
4, composite. 67, prime.
Mersenne primes are mostly of interest as mathematical curios. A Mersenne prime has the form 2n-1. For 2n-1 to be prime, n must also be prime. Perfect numbers have the form 2n-1(2n-1) where 2n-1 is a Mersenne prime, so when a new Mersenne prime is discovered, another perfect number is also found.
Prime
1 is special 2 prime 3 prime 4 composite 5 prime 6 composite 7 prime 8 composite 9 composite 10 composite 11 prime 12 composite ext.
5 prime, 25 composite.
Prime.
It is a composite number.