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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
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
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", "))
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