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%I #5 Mar 31 2012 13:22:03
%S 2,2,2,6,20,14,32,90,72,80,230,80,560,740,1542,1782,450,828,2562,3936,
%T 12474,9288,10224,16022,11088,31034,53972,92372
%N Nearest k to j such that k*(2^j-1)-1 is prime where j=A000043(n) and 2^j-1 = Mersenne-prime(n) = A000668(n). If there are two k values equidistant from j, each of which produces a prime, the larger of the two gets added to the sequence.
%e n=7, j=A000043(7)=19, A000668(7)=524287, then k=6 or k=32 are the nearest values to j which produce primes so we take the larger of the two k values for a(7)=32.
%Y Cf. A000043, A000668, A098555, A159585.
%K hard,nonn
%O 1,1
%A _Pierre CAMI_, Jan 16 2005
%E a(5)=20, a(20)=3936 corrected, other terms verified, a(27)-a(28) extended by _Ray Chandler_, Apr 16 2009