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.
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.
