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A291350
Numbers k such that k!4 + 2^9 is prime, where k!4 = k!!!! is the quadruple factorial number (A007662).
1
9, 11, 13, 17, 19, 21, 29, 31, 33, 35, 67, 103, 111, 129, 179, 355, 713, 799, 921, 1013, 1389, 1543, 2097, 2287, 3657, 4115, 7031, 10689, 11715, 16401, 16893, 19497, 29737, 35615
OFFSET
1,1
COMMENTS
Corresponding primes are: 557, 743, 1097, 10457, 66347, 209357, 151413137, ...
a(35) > 10^5.
Terms > 35 correspond to probable primes.
EXAMPLE
11!4 + 2^9 = 11*7*3*1 + 512 = 743 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[#, 4] + 2^9] &]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Aug 22 2017
STATUS
approved