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A289687
Numbers k such that k!6 - 9 is prime, where k!6 is the sextuple factorial number (A085158).
1
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
OFFSET
1,1
COMMENTS
Corresponding primes are: 7, 31, 631, 14071, 116471, 24663654391, 1282510028791, ...
a(30) > 10^5.
Terms > 46 correspond to probable primes.
EXAMPLE
16!6 - 9 = 16*10*4 - 8 = 631 is prime, so 16 is in the sequence.
MATHEMATICA
MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[8, 50000], PrimeQ[MultiFactorial[#, 6] - 9] &]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jul 09 2017
EXTENSIONS
a(27)-a(29) from Robert Price, Aug 03 2018
STATUS
approved