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A247463
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Numbers n such that n!3 - 3^3 is prime, where n!3 = n!!! is a triple factorial number (A007661).
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1
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8, 11, 13, 22, 29, 49, 56, 61, 103, 142, 149, 257, 319, 365, 680, 736, 737, 749, 947, 974, 1040, 4277, 4678, 9961, 10652, 15545, 18064, 31325, 34918, 41032
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OFFSET
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1,1
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COMMENTS
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Large terms correspond to probable primes.
a(31) > 50000.
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LINKS
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EXAMPLE
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11!3-27 = 11*8*5*2-27 = 853 is prime, so 11 is in the sequence.
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MATHEMATICA
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MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]];
lst={}; Do[If[PrimeQ[MultiFactorial[n, 3] - 27], AppendTo[lst, n]], {n, 100}]; lst
Select[Range[6, 1100], PrimeQ[Times@@Range[#, 1, -3]-27]&] (* Harvey P. Dale, Mar 16 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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STATUS
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approved
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