A204661 Numbers n such that n!8+1 is prime (for n!8 see A114800).

0, 1, 2, 4, 6, 28, 30, 46, 60, 72, 86, 90, 112, 154, 162, 206, 280, 354, 400, 512, 606, 614, 678, 790, 938, 1054, 1092, 1148, 1582, 1788, 2088, 2206, 2598, 2912, 3672, 4642, 6272, 6428, 7084, 7604, 8580, 9464, 12762, 18386, 24910, 30448, 31696, 40288, 41682, 45730

Offset

1,3

Comments

n!8 = A114800(n).

No other terms < 50000. - Robert Price, Jul 29 2012

Links

Table of n, a(n) for n=1..50.

Ken Davis, Status of Search for Multifactorial Primes.

Ken Davis, Results for n!8+1.

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 1000], PrimeQ[MultiFactorial[#, 8] + 1] & ] (* Robert Price, Apr 19 2019 *)
Select[Range[0, 46000], PrimeQ[Times@@Range[#, 1, -8]+1]&] (* Harvey P. Dale, Apr 12 2022 *)

Prog

(PARI) for(n=0, 9999, isprime(prod(i=0, (n-2)\8, n-8*i)+1)& print1(n", "))

Crossrefs

Cf. A204657, A204658, A204659, A204660, A204662, A204663, A204664, A156165, A156167, A085150, A085148, A085146, A037083, A080778, A002981.

Sequence in context: A318609 A195333 A106274 * A284919 A279419 A077633

Adjacent sequences: A204658 A204659 A204660 * A204662 A204663 A204664

Keyword

nonn,hard

Author

M. F. Hasler, Jan 17 2012

Extensions

a(35)-a(50) from Robert Price, Jul 29 2012

Status

approved