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A204659 Numbers n such that n!9-1 is prime. 9
3, 4, 6, 8, 15, 20, 23, 27, 30, 44, 51, 62, 80, 90, 95, 114, 129, 138, 150, 152, 156, 182, 201, 216, 293, 332, 342, 393, 411, 414, 419, 525, 668, 743, 800, 972, 1034, 1266, 1785, 1869, 2777, 3561, 3780, 4106, 4328, 4428, 4556, 4574, 4629, 5001, 5397, 6315 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n!9 = A114806(n).

a(74) > 50000. - Robert Price, Jun 14 2012

a(1)-a(73) are proved prime by the deterministic test of pfgw. - Robert Price, Jun 14 2012

LINKS

Robert Price, Table of n, a(n) for n = 1..81

Ken Davis, Status of Search for Multifactorial Primes.

Ken Davis, Results for n!9-1.

MATHEMATICA

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

Select[Range[1000], PrimeQ[MultiFactorial[#, 9] - 1] & ] (* Robert Price, Apr 19 2019 *)

PROG

(PARI) for(n=0, 9999, isprime(prod(i=0, (n-2)\9, n-9*i)-1)& print1(n", "))

CROSSREFS

Cf. A204657, A204658, A204660, A204661, A204662, A204663, A204664, A156165, A156167, A085150, A085148, A085146, A037083, A080778, A002981.

Sequence in context: A242870 A025073 A325432 * A134580 A007749 A063506

Adjacent sequences:  A204656 A204657 A204658 * A204660 A204661 A204662

KEYWORD

nonn,hard

AUTHOR

M. F. Hasler, Jan 17 2012

EXTENSIONS

a(47)-a(73) from Robert Price, Jun 14 2012

Extended b-file adding a(74)-a(81) using data from Ken Davis link by Robert Price, Apr 19 2019

STATUS

approved

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Last modified August 9 13:57 EDT 2020. Contains 336323 sequences. (Running on oeis4.)