A135972 Nonprime numbers of the form 2^n - 1.

0, 1, 15, 63, 255, 511, 1023, 2047, 4095, 16383, 32767, 65535, 262143, 1048575, 2097151, 4194303, 8388607, 16777215, 33554431, 67108863, 134217727, 268435455, 536870911, 1073741823, 4294967295, 8589934591, 17179869183, 34359738367

Offset: 1

Author

Artur Jasinski, Dec 09 2007

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..3301

Crossrefs

Subsequence of A000225.

Programs

Maple

remove(isprime, [seq(2^n-1,n=0..100)]); # Robert Israel, Dec 28 2015

Mathematica

k = {}; Do[If[ ! PrimeQ[2^n - 1], AppendTo[k, 2^n - 1]], {n, 1, 100}]; k

PARI

lista(nn) = for (n=0, nn, if (! isprime(np = 2^n-1), print1(np, ", "))); \\ Michel Marcus, Nov 04 2013