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A103538
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Numbers k such that prime(k)*prime(k)# - 1 is prime, where prime(k)# is the k-th primorial.
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0
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1, 2, 3, 5, 6, 7, 13, 16, 20, 23, 64, 191, 490, 3620, 5909
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OFFSET
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1,2
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LINKS
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MATHEMATICA
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q[n_] := PrimeQ[Prime[n]*Product[Prime[i], {i, 1, n}] - 1]; Select[Range[500], q] (* Amiram Eldar, Jul 18 2021 *)
Module[{nn=500, p1, p2}, p1=Prime[Range[nn]]; p2=FoldList[Times, p1]; Select[Thread[ {p1, p2}], PrimeQ[ Times@@#-1]&][[;; , 1]]]//PrimePi (* Harvey P. Dale, May 21 2023 *)
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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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STATUS
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approved
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