A183185 Numbers n such that 10^(2n+1)-5*10^n-1 is prime.

14, 22, 36, 104, 1136, 17864, 25448

Offset: 1

Author

Ray Chandler, Dec 28 2010

Keywords

• nonn
• base

References

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

Links

• Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
• Makoto Kamada, Prime numbers of the form 99...99499...99
• Index entries for primes involving repunits.

Crossrefs

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

Programs

Mathematica

Do[If[PrimeQ[10^(2n + 1) - 5*10^n - 1], Print[n]], {n, 3000}]

PARI

is(n)=ispseudoprime(10^(2*n+1)-5*10^n-1) \\ Charles R Greathouse IV, Jun 13 2017

Formula

a(n) = (A077782(n)-1)/2.