cp's OEIS Frontend

A204658 Numbers n such that n!10-1 is prime.

%I A204658 #25 Nov 12 2019 11:34:32
%S A204658 3,4,6,8,12,20,40,48,60,62,70,84,88,168,240,258,372,760,932,1010,2110,
%T A204658 2464,2490,2702,3180,4744,6024,8858,9060,10322,13382,15778,19322,
%U A204658 22372,22928,25344,28050,40604,42282,45884,52428,58250,81220,93612,108650
%N A204658 Numbers n such that n!10-1 is prime.
%C A204658 n!10 = product( n-10k, 0 <= k < n/10 ).
%C A204658 See also links in A156165.
%C A204658 a(1)-a(40) are proved prime by deterministic tests of pfgw. - _Robert Price_, Jun 11 2012
%C A204658 a(41) > 50000. - _Robert Price_, Jun 11 2012
%H A204658 Ken Davis, <a href="http://mfprimes.free-dc.org">Status of Search for Multifactorial Primes</a>.
%H A204658 Ken Davis, <a href="http://mfprimes.free-dc.org/mfdata/f10m.html">Results for n!10-1.</a>
%t A204658 MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
%t A204658 Select[Range[1000], PrimeQ[MultiFactorial[#, 10] - 1] & ] (* _Robert Price_, Apr 19 2019 *)
%o A204658 (PARI) for(n=0,9999,isprime(prod(i=0,(n-2)\10,n-10*i)-1)& print1(n","))
%Y A204658 Cf. A204657, A204659, A204660, A204661, A204662, A204663, A204664, A156165, A156167, A085150, A085148, A085146, A037083, A080778, A002981.
%K A204658 nonn,hard
%O A204658 1,1
%A A204658 _M. F. Hasler_, Jan 17 2012
%E A204658 a(26)-a(40) from _Robert Price_, Jun 11 2012
%E A204658 a(41)-a(45) from Ken Davis link entered by _Robert Price_, Apr 19 2019