A145851 Primes of the form k followed by k 9's.

19, 49999, 599999, 1799999999999999999, 2099999999999999999999, 289999999999999999999999999999

Offset: 1

Author

Lekraj Beedassy, Oct 21 2008

Keywords

• nonn
• base

Comments

Corresponding k, which cannot be multiples of 3, are in A174352. The next term has 176 digits, too large to include here. - Rick L. Shepherd, Mar 22 2010

Crossrefs

Cf. A141311, A145852.

Cf. A174352. - Rick L. Shepherd, Mar 22 2010

Programs

Mathematica

Select[Table[FromDigits[PadRight[{k},k+1,9]],{k,200}],PrimeQ] (* Harvey P. Dale, Jun 22 2022 *)

PARI

lista(nn) = for(k=1, nn, if(ispseudoprime(q=k*10^(k-1)-1), print1(q, ", "))); \\ Jinyuan Wang, Mar 24 2020

Extensions

a(2) was 4999; corrected by Rick L. Shepherd, Mar 22 2010