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A098817
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a(n) is the least k such that k*Mersenne_prime(n)^2 - 1 and k*Mersenne_prime(n)^2 + 1 are twin primes.
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0
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2, 18, 72, 780, 228, 852, 228, 1080, 4020, 25800, 6012, 40332, 713502, 332880, 455892, 6428118, 4142652, 173808
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OFFSET
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1,1
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LINKS
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EXAMPLE
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2*((2^2-1)^2) - 1 = 17, 2*((2^2-1)^2) + 1 = 19; 17 and 19 are twin primes so a(1) = 2.
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MATHEMATICA
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f[p_] := Module[{k = 1}, While[!PrimeQ[k*p^2 - 1] || !PrimeQ[k*p^2 + 1], k++]; k]; f /@ (2^MersennePrimeExponent[Range[10]] - 1) (* Amiram Eldar, Aug 28 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(7) corrected, a(12) inserted and a(15)-a(18) added by Amiram Eldar, Aug 28 2021
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STATUS
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approved
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