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A289696 Numbers k such that k!6 - 18 is prime, where k!6 is the sextuple factorial number (A085158). 1
11, 13, 23, 25, 35, 85, 89, 91, 103, 127, 161, 265, 295, 385, 605, 719, 913, 1379, 1423, 1481, 1603, 2129, 2603, 3893, 4739, 6461, 7249, 7549, 8149, 10633, 14447, 27463, 30323, 33991, 35821, 42221, 46525, 59057 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding primes are: 37, 73, 21487, 43207, 21827557, 11510631741140058401857, ...

a(39) > 10^5.

Terms > 35 correspond to probable primes.

LINKS

Table of n, a(n) for n=1..38.

Henri & Renaud Lifchitz, PRP Records. Search for n!6-18.

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

EXAMPLE

13!6 - 18 = 13*7 - 18 = 73 is prime, so 13 is in the sequence.

MATHEMATICA

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

Select[Range[9, 50000], PrimeQ[MultiFactorial[#, 6] - 18] &]

Select[Range[11, 60000], PrimeQ[Times@@Range[#, 1, -6]-18]&] (* Harvey P. Dale, Aug 10 2019 *)

CROSSREFS

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

Sequence in context: A160373 A091998 A208296 * A023232 A075519 A019406

Adjacent sequences:  A289693 A289694 A289695 * A289697 A289698 A289699

KEYWORD

nonn,more

AUTHOR

Robert Price, Jul 09 2017

EXTENSIONS

a(38) from Robert Price, Aug 03 2018

STATUS

approved

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Last modified November 22 00:32 EST 2019. Contains 329383 sequences. (Running on oeis4.)