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%I #5 Mar 11 2014 01:34:12
%S 3,21,465,8001,33542145,8589737985,137438167041,2305843005992468481,
%T 2658455991569831742348849606740148225,
%U 191561942608236107294793377465333618488307184098607105
%N M(M-1)/2, where M is Mersenne prime A000668(n).
%C Perfect number A000396(n) minus Mersenne prime A000668(n).
%H Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos"</a>.
%F a(n)=A000668(n)*(A000668(n)-1)/2. Also a(n)=A000396(n)-A000668(n).
%Y Cf. A000217, A000396, A000668, A036689, A139096, A139115, A139116, A139223, A139225, A139226, A139256, A139306.
%K nonn
%O 1,1
%A _Omar E. Pol_, May 10 2008
%E More terms from _Max Alekseyev_, Mar 09 2009
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