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%I #6 Oct 15 2013 22:31:28
%S 2,5,29,113,8179,131063,524269,2147483629,2305843009213693921,
%T 618970019642690137449562091,162259276829213363391578010287957,
%U 170141183460469231731687303715884105703
%N Prime preceding n-th Mersenne-prime. PrevPrime[n-th Mersenne prime]=PrevPrime[A000668].
%F a(n)=Prime[PrimePi[M(n)]-1]=Prime[PrimePi[A000668(n)]-1]
%t NextPrime[Select[2^Prime[Range[50]] - 1, PrimeQ], -1] (* _Jayanta Basu_, Jul 08 2013 *)
%K nonn
%O 1,1
%A _Labos Elemer_, Aug 05 2002
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