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A289687
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Numbers k such that k!6 - 9 is prime, where k!6 is the sextuple factorial number (A085158).
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1
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8, 10, 16, 22, 26, 46, 52, 56, 70, 74, 286, 302, 308, 484, 698, 1100, 1226, 1528, 2486, 3796, 4256, 8524, 10688, 19424, 22226, 49346, 53746, 64178, 84304
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OFFSET
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1,1
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COMMENTS
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Corresponding primes are: 7, 31, 631, 14071, 116471, 24663654391, 1282510028791, ...
a(30) > 10^5.
Terms > 46 correspond to probable primes.
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LINKS
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Table of n, a(n) for n=1..29.
Henri & Renaud Lifchitz, PRP Records. Search for n!6-9.
Joe McLean, Interesting Sources of Probable Primes
OpenPFGW Project, Primality Tester
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EXAMPLE
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16!6 - 9 = 16*10*4 - 8 = 631 is prime, so 16 is in the sequence.
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MATHEMATICA
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MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[8, 50000], PrimeQ[MultiFactorial[#, 6] - 9] &]
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CROSSREFS
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Cf. A007661, A037082, A084438, A123910, A242994.
Sequence in context: A270796 A058633 A165143 * A155966 A228072 A038209
Adjacent sequences: A289684 A289685 A289686 * A289688 A289689 A289690
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KEYWORD
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nonn,more
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AUTHOR
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Robert Price, Jul 09 2017
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EXTENSIONS
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a(27)-a(29) from Robert Price, Aug 03 2018
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STATUS
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approved
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