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A204658 Numbers n such that n!10-1 is prime. 8
3, 4, 6, 8, 12, 20, 40, 48, 60, 62, 70, 84, 88, 168, 240, 258, 372, 760, 932, 1010, 2110, 2464, 2490, 2702, 3180, 4744, 6024, 8858, 9060, 10322, 13382, 15778, 19322, 22372, 22928, 25344, 28050, 40604, 42282, 45884, 52428, 58250, 81220, 93612, 108650 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n!10 = product( n-10k, 0 <= k < n/10 ).

See also links in A156165.

a(1)-a(40) are proved prime by deterministic tests of pfgw. - Robert Price, Jun 11 2012

a(41) > 50000. - Robert Price, Jun 11 2012

LINKS

Table of n, a(n) for n=1..45.

Ken Davis, Status of Search for Multifactorial Primes.

Ken Davis, Results for n!10-1.

MATHEMATICA

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

Select[Range[1000], PrimeQ[MultiFactorial[#, 10] - 1] & ] (* Robert Price, Apr 19 2019 *)

PROG

(PARI) for(n=0, 9999, isprime(prod(i=0, (n-2)\10, n-10*i)-1)& print1(n", "))

CROSSREFS

Cf. A204657, A204659, A204660, A204661, A204662, A204663, A204664, A156165, A156167, A085150, A085148, A085146, A037083, A080778, A002981.

Sequence in context: A145751 A277099 A146566 * A139041 A244607 A136483

Adjacent sequences:  A204655 A204656 A204657 * A204659 A204660 A204661

KEYWORD

nonn,hard

AUTHOR

M. F. Hasler, Jan 17 2012

EXTENSIONS

a(26)-a(40) from Robert Price, Jun 11 2012

a(41)-a(45) from Ken Davis link entered by Robert Price, Apr 19 2019

STATUS

approved

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Last modified January 18 14:07 EST 2021. Contains 340254 sequences. (Running on oeis4.)