A139057 Primes of the form (k!-3)/3.

7, 239, 159667199, 6974263295999, 2947253997913233984847871999999, 98410933013201380282539536547839999999, 20138421021124611879118377356171332502421503999999999

Offset: 1

Author

Artur Jasinski, Apr 07 2008

Keywords

• nonn

Comments

Numbers k for which (k! - 3)/3 is prime see A139056.

a(8) is 180 decimal digits long. See formula for more terms. - Derek Orr, Mar 28 2014

Crossrefs

Cf. A089085, A117141, A007749, A139056.

Programs

Mathematica

a = {}; Do[If[PrimeQ[(-3 + n!)/3], AppendTo[a, (-3 + n!)/3]], {n, 1, 100}]; a
Select[(Range[50]!-3)/3,PrimeQ] (* Harvey P. Dale, Nov 27 2015 *)

PARI

for(n=1,1000,if(floor(n!/3-1)==n!/3-1,if(ispseudoprime(n!/3-1),print(n!/3-1)))) \\ Derek Orr, Mar 28 2014

Formula

a(n) = (A139056(n)!-3)/3 for all n. - Derek Orr, Mar 28 2014

Extensions

Definition corrected by Derek Orr, Mar 28 2014