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A154666
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Numbers k such that k-1, k+1, and k^2-k-1 are primes.
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3
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4, 6, 12, 42, 60, 102, 150, 192, 282, 420, 432, 462, 570, 660, 810, 882, 1062, 1230, 1320, 1872, 1950, 2550, 2712, 2730, 3120, 3252, 4020, 4092, 6090, 8220, 8862, 8970, 9042, 9240, 9720, 10140, 10530, 10710, 11550, 11832, 11970, 12252, 13680, 13902
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OFFSET
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1,1
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COMMENTS
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Note that k-1 and k+1 are twin primes and the third prime is (k-1)*(k+1)-k, the product of the twin primes minus their average.
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LINKS
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EXAMPLE
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3*5 - 4 = 11.
5*7 - 6 = 29.
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MATHEMATICA
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lst={}; Do[If[PrimeQ[n-1]&&PrimeQ[n+1], If[PrimeQ[(n-1)*(n+1)-n], AppendTo[lst, n]]], {n, 8!}]; lst
Mean/@Select[Select[Partition[Prime[Range[2000]], 2, 1], Last[#]-First[#]==2&], PrimeQ[Times@@#-Mean[#]]&] (* Harvey P. Dale, Mar 17 2011 *)
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PROG
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(Magma) [k:k in [2..15000]| IsPrime(k-1) and IsPrime(k+1)and IsPrime(k^2-k-1)]; // Marius A. Burtea, Dec 21 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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