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A287956
Numbers k such that k!6 + 6 is prime, where k!6 is the sextuple factorial number (A085158 ).
1
1, 5, 7, 11, 13, 17, 37, 43, 55, 107, 139, 149, 157, 211, 223, 343, 373, 409, 523, 12049, 16457, 17143, 17543, 18391, 25829, 25945, 31307, 34601, 41687
OFFSET
1,2
COMMENTS
Corresponding primes are: 7, 11, 13, 61, 97, 941, 49579081, 2131900231, 5745471106381, ...
a(43) > 50000.
Terms > 35 correspond to probable primes.
EXAMPLE
11!6 + 6 = 11*5 + 6 = 61 is prime, so 11 is in the sequence.
MATHEMATICA
MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 6] + 6] &]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 03 2017
STATUS
approved