A183182 Numbers k such that (7*10^(2*k+1) + 9*10^k - 7)/9 is prime.

1, 3, 39, 54, 168, 240, 5328, 6159, 24675, 52227, 113887, 152761

Offset

1,2

References

C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

Links

Table of n, a(n) for n=1..12.

Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's).

Makoto Kamada, Prime numbers of the form 77...77877...77.

Index entries for primes involving repunits.

Formula

a(n) = (A077793(n) - 1)/2.

Mathematica

Do[If[PrimeQ[(7*10^(2n + 1) + 9*10^n - 7)/9], Print[n]], {n, 3000}]

Prog

(PARI) is(n)=ispseudoprime((7*10^(2*n+1)+9*10^n-7)/9) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.

Sequence in context: A213004 A359081 A163789 * A277713 A134106 A153875

Adjacent sequences: A183179 A183180 A183181 * A183183 A183184 A183185

Keyword

nonn,more,base

Author

Ray Chandler, Dec 28 2010

Extensions

a(9) from Robert Price, Oct 07 2023

a(10) from Robert Price, Oct 30 2023

a(11) from Robert Price, Aug 03 2024

a(12) from Robert Price, Jun 24 2026

Status

approved