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A098819
Least k such that k*(Mersenne_prime(n)^2) + 1 is prime.
0
2, 4, 16, 12, 22, 28, 30, 22, 138, 12, 102, 180, 426, 1444, 9502, 6568, 2212, 5380, 9942, 3034, 24222, 31530, 2962, 7848, 93280, 3718
OFFSET
1,1
COMMENTS
Subsequence of A035092. - Amiram Eldar, Mar 01 2019
EXAMPLE
2*((2^2-1)^2)+1=19 prime so a(1)=2.
MATHEMATICA
a[n_] := Module[{k = 1, m = (2^MersennePrimeExponent[n] - 1)^2}, While[! PrimeQ[k*m + 1], k++]; k]; Array[a, 20] (* Amiram Eldar, Mar 01 2019 *)
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Pierre CAMI, Oct 08 2004
EXTENSIONS
a(19)-a(22) from Donovan Johnson, Mar 23 2008
a(23)-a(26) from Amiram Eldar, Mar 01 2019
STATUS
approved