A139205 Numbers k such that (k!-10)/10 is prime.

5, 6, 7, 11, 13, 17, 28, 81, 87, 433, 640, 647, 798, 1026, 1216, 1277, 3825, 6684

Offset: 1

Author

Artur Jasinski, Apr 11 2008

Keywords

• hard
• more
• nonn

Comments

a(19) > 25000. - Robert Price, Dec 23 2016

Crossrefs

Cf. A139189, A139190, A139191, A139192, A139193, A139194, A139195, A139196, A139197, A139198.

Cf. n!/m-1 is a prime: A002982, A082671, A139056, A139199-A139205; n!/m+1 is a prime: A002981, A082672, A089085, A139061, A139058, A139063, A139065, A151913, A137390, A139071 (1<=m<=10).

Programs

Mathematica

a = {}; Do[If[PrimeQ[(n! - 10)/10], Print[a]; AppendTo[a, n]], {n, 1, 300}]; a (*Artur Jasinski*)
Select[Range[700],PrimeQ[(#!-10)/10]&] (* Harvey P. Dale, Feb 15 2015 *)

Extensions

One additional term (a(12)) from Harvey P. Dale, Feb 15 2015

More terms from Serge Batalov, Feb 18 2015

a(18) from Robert Price, Dec 23 2016