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A291344
Numbers k such that k!4 + 2^4 is prime, where k!4 = k!!!! is the quadruple factorial number (A007662).
1
0, 1, 3, 7, 9, 13, 19, 27, 35, 37, 65, 67, 75, 83, 89, 101, 111, 229, 363, 633, 1605, 1663, 1769, 1863, 1947, 2695, 3003, 5309, 7835, 9495, 9945, 11041, 18833, 21119, 21465, 21889, 24509, 26757, 27595, 33657, 54007, 67699, 87915
OFFSET
1,3
COMMENTS
Corresponding primes are: 17, 17, 19, 37, 61, 601, 65851, 40883551, ...
a(44) > 10^5.
Terms > 37 correspond to probable primes.
EXAMPLE
13!4 + 2^4 = 13*9*5*1 + 16 = 601 is prime, so 13 is in the sequence.
MATHEMATICA
MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 4] + 2^4] &]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Aug 22 2017
EXTENSIONS
a(41)-a(43) from Robert Price, Sep 25 2019
STATUS
approved