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 A289547 Numbers k such that k!6 - 4 is prime, where k!6 is the sextuple factorial number (A085158 ). 1
 6, 7, 9, 15, 21, 27, 29, 321, 327, 333, 567, 1025, 4263, 4365, 5175, 5655, 9221, 9327, 9681, 19685, 24777, 57869, 58737 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Corresponding primes are: 2, 3, 23, 401, 8501, 229631, 623641, ... a(24) > 10^5. Terms > 29 correspond to probable primes. LINKS Henri & Renaud Lifchitz, PRP Records. Search for n!6-4. Joe McLean, Interesting Sources of Probable Primes OpenPFGW Project, Primality Tester EXAMPLE 15!6 - 4 = 15*9*3 - 4 = 401 is prime, so 15 is in the sequence. MATHEMATICA MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]]; Select[Range[4, 50000], PrimeQ[MultiFactorial[#, 6] - 4] &] CROSSREFS Cf. A007661, A037082, A084438, A123910, A242994. Sequence in context: A045014 A047591 A239869 * A329912 A187922 A032456 Adjacent sequences:  A289544 A289545 A289546 * A289548 A289549 A289550 KEYWORD nonn,more AUTHOR Robert Price, Jul 07 2017 EXTENSIONS a(22)-a(23) from Robert Price, Aug 03 2018 STATUS approved

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Last modified January 21 16:22 EST 2020. Contains 331114 sequences. (Running on oeis4.)