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A104038
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a(n) is the least k such that k*(k+1)*Mersenne-prime(n)+1 is prime.
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0
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1, 2, 3, 12, 8, 3, 5, 14, 17, 69, 189, 42, 392, 167, 377, 12, 2007, 434, 744, 705, 1089, 1109, 7833, 7328, 1271, 192, 6770, 2379
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OFFSET
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1,2
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LINKS
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EXAMPLE
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1*2*(2^2-1)+1 = 7 is prime, so a(1) = 1.
2*3*(2^3-1)+1 = 43 is prime, so a(2) = 2.
3*4*(2^5-1)+1 = 373 is prime, so a(3) = 3.
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MATHEMATICA
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f[p_] := Module[{k = 1}, While[! PrimeQ[k*(k + 1)*p + 1], k++]; k]; f /@ (2^MersennePrimeExponent[Range[15]] - 1) (* Amiram Eldar, Jul 18 2021 *)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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a(14) inserted and a(24)-a(28) added by Amiram Eldar, Jul 18 2021
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STATUS
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approved
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