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2^n - 1 (A000225) where n is nonprime number (A141468).
0

%I #2 Mar 31 2012 10:24:25

%S 0,1,15,63,127,255,511,1023,4095,16383,32767,65535,262143,1048575,

%T 2097151,4194303,16777215,33554431,67108863,134217727,268435455,

%U 1073741823,4294967295

%N 2^n - 1 (A000225) where n is nonprime number (A141468).

%C a(0) = 0 since 2^0 - 1 = 0 and 0 is nonprime, a(1) = 1 since 2^1 - 1 = 1 and 1 is nonprime, a(2) = 15 since 2^4 - 1 = 15 and 4 is nonprime, ...

%Y A000668

%K nonn

%O 0,3

%A _Jani Melik_, Mar 10 2009