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A289685 Numbers k such that k!6 - 6 is prime, where k!6 is the sextuple factorial number (A085158). 1
17, 19, 23, 31, 37, 47, 65, 151, 157, 251, 283, 371, 391, 635, 779, 799, 1517, 1799, 3355, 24619, 40375, 40793, 53135, 79427 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding primes are: 929, 1723, 21499, 1339969, 49579069, 42061737019, ...

a(25) > 10^5.

Terms > 65 correspond to probable primes.

LINKS

Table of n, a(n) for n=1..24.

Henri & Renaud Lifchitz, PRP Records. Search for n!6-6.

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

EXAMPLE

17!6 - 6 = 17*11*5 - 6 = 929 is prime, so 17 is in the sequence.

MATHEMATICA

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];

Select[Range[6, 50000], PrimeQ[MultiFactorial[#, 6] - 6] &]

CROSSREFS

Cf. A007661, A037082, A084438, A123910, A242994.

Sequence in context: A140947 A205700 A228070 * A144487 A108266 A102325

Adjacent sequences:  A289682 A289683 A289684 * A289686 A289687 A289688

KEYWORD

nonn,more

AUTHOR

Robert Price, Jul 09 2017

EXTENSIONS

a(23)-a(24) from Robert Price, Aug 03 2018

STATUS

approved

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Last modified May 15 18:26 EDT 2021. Contains 343920 sequences. (Running on oeis4.)