1,3

Table of n, a(n) for n=1..71.

Complement of A000043.

8 belongs to the sequence because 2^8-1=255 is not a prime.

Select[Range[0, 100], !PrimeQ[2^#-1]&] (* Harvey P. Dale, Mar 22 2011 *)

(MAGMA) [n: n in [0..100]| not IsPrime(2^n-1)] // Vincenzo Librandi, Jan 28 2011

Cf. A000043 (Mersenne prime exponents), A054723 (primes of this sequence).

Sequence in context: A091985 A091984 A228651 * A320985 A047748 A299540

Adjacent sequences: A045759 A045760 A045761 * A045763 A045764 A045765

nonn,easy,nice

Felice Russo

More terms from Jennifer D. Secor (s1175994(AT)cedarville.edu)

approved