%I #13 Dec 29 2015 02:24:46
%S 0,1,15,63,255,511,1023,2047,4095,16383,32767,65535,262143,1048575,
%T 2097151,4194303,8388607,16777215,33554431,67108863,134217727,
%U 268435455,536870911,1073741823,4294967295,8589934591,17179869183,34359738367
%N Nonprime numbers of the form 2^n - 1.
%H Robert Israel, <a href="/A135972/b135972.txt">Table of n, a(n) for n = 1..3301</a>
%p remove(isprime, [seq(2^n-1,n=0..100)]); # _Robert Israel_, Dec 28 2015
%t k = {}; Do[If[ ! PrimeQ[2^n - 1], AppendTo[k, 2^n - 1]], {n, 1, 100}]; k
%o (PARI) lista(nn) = for (n=0, nn, if (! isprime(np = 2^n-1), print1(np, ", "))); \\ _Michel Marcus_, Nov 04 2013
%Y Subsequence of A000225.
%K nonn
%O 1,3
%A _Artur Jasinski_, Dec 09 2007
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