A178488 Numbers k such that 8*k! + 1 is prime.

2, 4, 9, 10, 11, 12, 15, 25, 31, 46, 53, 78, 318, 615, 955, 1646, 2669, 2672, 3515, 7689

Offset: 1

Author

Robert G. Wilson v, Sep 13 2010 and M. F. Hasler, Sep 16 2010

Keywords

• nonn
• hard
• more

Comments

a(20) > 3810. - Jinyuan Wang, Feb 05 2020

a(21) > 12000. - Michael S. Branicky, Jul 03 2024

Links

• Index entries for sequences related to numbers of primes of the form k*n!+-1

Crossrefs

Cf. A002981, A051915, A076679, A076680, A076681, A076682, A076683, A180626, A126896.

Programs

Mathematica

fQ[n_] := PrimeQ[8 n! + 1]; k = 0; lst = {}; While[k < 1501, If[ fQ@k, AppendTo[lst, k]; Print@k]; k++ ]; lst

PARI

for(k=1, 999, ispseudoprime(8*k!+1) & print1(k, ", "))

PFGW

ABC2 8*$a!+1
a: from 1 to 1000 // Jinyuan Wang, Feb 05 2020

Extensions

a(16)-a(19) from Jinyuan Wang, Feb 05 2020

a(20) from Michael S. Branicky, Jul 02 2024