A108654 Numbers k such that 10^k - 117 is prime.

3, 4, 6, 7, 9, 15, 27, 40, 72, 134, 170, 204, 237, 240, 285, 288, 592, 613, 1443, 1524, 2289, 2292, 16326, 19492, 31498, 35312

Offset

1,1

Links

Table of n, a(n) for n=1..26.

Example

If k=3 then 10^k - 117 = 883 (prime).
If k=40 then 10^k - 117 = 9999999999999999999999999999999999999883 (prime).

Maple

a := proc (n) if isprime(10^n-117) = true then n else end if end proc; seq(a(n), n = 1 .. 1500); # Emeric Deutsch, Jul 09 2007

Mathematica

Select[Range[3, 2500], PrimeQ[10^#-117]&]  (* Harvey P. Dale, Feb 18 2011 *)

Prog

(PARI) is(n)=ispseudoprime(10^n-117) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A066271 A127594 A094604 * A131530 A285379 A102093

Adjacent sequences: A108651 A108652 A108653 * A108655 A108656 A108657

Keyword

nonn,hard,more

Author

Parthasarathy Nambi, Jul 06 2005

Extensions

a(9)-a(19) from Emeric Deutsch, Jul 09 2007

a(20)-a(22) from Harvey P. Dale, Feb 18 2011

a(23)-a(24) from Michael S. Branicky, Apr 01 2023

a(25)-a(26) from Michael S. Branicky, Oct 29 2024

Status

approved