A097954 Numbers k such that 7*10^k + 9 is prime.

1, 2, 4, 6, 11, 12, 13, 35, 46, 57, 128, 156, 263, 353, 396, 429, 783, 982, 1058, 1563, 1695, 1816, 1937, 4236, 4431, 6858, 9898, 13145, 16646, 20891, 63351, 105296, 113693, 121144, 163780, 234915, 284751

Offset

1,2

Comments

a(38) > 3*10^5. - Robert Price, Jul 10 2023

Links

Table of n, a(n) for n=1..37.

Makoto Kamada, Prime numbers of the form 700...009.

Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.

Index entries for primes involving repunits.

Formula

a(n) = A101130(n) + 1.

Example

k=2 we get 7*10^2+9 = 7*100+9 = 709, which is prime.

Mathematica

Do[ If[ PrimeQ[ 7*10^n + 9], Print[ n ]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 19 2005 *)
Select[Range[0, 10000], PrimeQ[7 10^# + 9] &] (* Vincenzo Librandi, Sep 06 2015 *)

Prog

(Magma) [n: n in [0..400] |IsPrime(7*10^n + 9)]; // Vincenzo Librandi, Sep 06 2015
(PARI) is(n)=ispseudoprime(7*10^n+9) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A101130.

Sequence in context: A063183 A057661 A237277 * A324333 A081988 A244748

Adjacent sequences: A097951 A097952 A097953 * A097955 A097956 A097957

Keyword

more,nonn

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Sep 05 2004

Extensions

a(19)-a(27) from Robert G. Wilson v, Jan 19 2005

a(28)-a(31) from Kamada data by Robert Price, Dec 14 2010

a(32)-a(35) from Robert Price, Sep 05 2015

a(36)-a(37) from Robert Price, Jul 10 2023

Status

approved