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 A082747 a(n) is the least k such that k*Mrs(n)*Mrs(n+1)*Mrs(n+2) + 1 is prime, where Mrs(n) is the n-th Mersenne prime. 0
 2, 4, 6, 4, 60, 280, 60, 210, 306, 154, 154, 538, 1272, 640, 4180, 6384, 12816, 2020, 10918, 9694, 45420, 47506, 11680, 1408 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..24. EXAMPLE 2*(2^2-1)*(2^3-1)*(2^5-1) + 1 = 1303 is prime, so a(1) = 2. MATHEMATICA f[n_] := Module[{k = 1}, While[! PrimeQ[k*n + 1], k++]; k]; f /@ Times @@@ Partition[2^MersennePrimeExponent[Range[15]] - 1, 3, 1] (* Amiram Eldar, Jul 18 2021 *) CROSSREFS Cf. A000043, A000668. Sequence in context: A353512 A257080 A099784 * A127275 A242796 A298527 Adjacent sequences: A082744 A082745 A082746 * A082748 A082749 A082750 KEYWORD nonn,hard,more AUTHOR Pierre CAMI, Oct 22 2004 EXTENSIONS a(11) inserted and a(17)-a(24) added by Amiram Eldar, Jul 18 2021 STATUS approved

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Last modified June 3 23:57 EDT 2023. Contains 363118 sequences. (Running on oeis4.)