The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #24 Oct 10 2021 22:45:03
%S 1,7,127,2047,524287,8388607,2147483647,34359738367,8796093022207,
%T 36028797018963967,576460752303423487,2361183241434822606847,
%U 604462909807314587353087,9671406556917033397649407,2475880078570760549798248447,10141204801825835211973625643007
%N a(n) = 2^(2*prime(n) - 3) - 1.
%F a(n) = A139286(n)/4 - 1.
%F a(n) = A000225(A131426(n)). - _Max Alekseyev_, Mar 07 2020
%F a(n) = A139290(n) - 1. - _Omar E. Pol_, Mar 10 2020
%t (2^(2#-1))/4-1&/@Prime[Range[20]] (* _Harvey P. Dale_, May 08 2011 *)
%Y Cf. A139286, A139287, A139288, A139289, A139290, A139293, A139294, A139306.
%K nonn
%O 1,2
%A _Omar E. Pol_, Apr 13 2008
%E Edited by _Max Alekseyev_, May 03 2009, Mar 07 2020