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a(n) = k-th prime, where k = n-th Mersenne prime = A000668(n).
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%I #7 Jan 21 2019 19:01:55

%S 5,17,127,709,84011,1742527,7754017,50685770143

%N a(n) = k-th prime, where k = n-th Mersenne prime = A000668(n).

%F a(n) = A000040(A000668(n)). [From _Omar E. Pol_, Dec 09 2009]

%t Prime[2^{2, 3, 5, 7, 13, 17, 19, 31} - 1] (* _Robert G. Wilson v_ *)

%o (PARI) prime(2^13-1) prime(2^7-1) prime(2^5-1) prime(2^3-1) prime(2^2-1)

%Y Cf. A000043, A000668.

%K hard,nonn

%O 1,1

%A _Jorge Coveiro_, Jan 31 2006

%E a(6)-a(8) from _Robert G. Wilson v_ and _Stefan Steinerberger_, Jan 31 2006

%E A-number in definition corrected by _Omar E. Pol_, Dec 09 2009