A105322 Primes of the form 8*10^n-7.

73, 7993, 799993, 7999993, 79999999993, 7999999999993, 79999999999993, 7999999999999999999999999999999999999993, 7999999999999999999999999999999999999999999999993

Offset: 1

Author

Farideh Firoozbakht, Apr 16 2005

Keywords

• nonn
• easy

Comments

This sequence is a subsequence of A104907 also is a subsequence of A105324(see A104907 and A105324).

Examples

			7993 is in the sequence because 7993=8*10^3-7 and 7993 is prime.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..16
• Makoto Kamada, Prime numbers of the form 799...993.

Crossrefs

Cf. A099190, A104907, A105324.

Programs

Magma

[ a: n in [0..50] | IsPrime(a) where a is 8*10^n-7 ]; // Vincenzo Librandi, Jul 19 2012

Mathematica

Do[If[PrimeQ[8*10^n - 7], Print[8*10^n - 7]], {n, 60}]
Select[Table[8*10^n-7,{n,0,80}],PrimeQ] (* Vincenzo Librandi, Jul 19 2012 *)

Formula

a(n) = 8*A099190(n) - 7.