%I

%S 7,2047,576460752303423487

%N 2^(2p - 1)/4-1, where p is a Mersenne prime A000668(n).

%F a(n) = 2^(2*A000668(n)-1)/4-1 = A139294(n)/4-1 = A139298(n)-1.

%K bref,nonn

%O 1,1

%A _Omar E. Pol_, Apr 13 2008