A098556
Least k such that k*Mersenne - prime(n) + 1 is prime.
Original entry on oeis.org
2, 4, 10, 4, 46, 12, 16, 46, 52, 136, 166, 114, 336, 154, 1474, 156, 1086, 1816, 2010, 9436, 1746, 3426, 6238, 40138, 858, 4018, 17262, 15418
Offset: 1
-
mexp = {the list in A000043}; f[n_] := Block[{k = 2, mp = 2^mexp[[n]] - 1}, While[ !PrimeQ[mp*k + 1] && k < 10000, k += 2 ]; If[k == 10000, 0, k]]; Do[ Print[ f[n]], {n, 21}] (* Robert G. Wilson v, Sep 17 2004 *)
a(21)=1746 corrected, other terms verified, a(23)-a(28) extended by
Ray Chandler, Apr 16 2009
A101416
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.
Original entry on oeis.org
2, 2, 2, 6, 20, 14, 32, 90, 72, 80, 230, 80, 560, 740, 1542, 1782, 450, 828, 2562, 3936, 12474, 9288, 10224, 16022, 11088, 31034, 53972, 92372
Offset: 1
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.
a(5)=20, a(20)=3936 corrected, other terms verified, a(27)-a(28) extended by
Ray Chandler, Apr 16 2009
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