A141311 Primes consisting of a digit and a nonempty string of 9's (i.e., primes of the form k*10^m - 1, where k is any digit).

19, 29, 59, 79, 89, 199, 499, 599, 1999, 2999, 4999, 8999, 49999, 59999, 79999, 199999, 599999, 799999, 2999999, 4999999, 19999999, 29999999, 59999999, 89999999, 799999999, 59999999999, 79999999999, 59999999999999, 499999999999999, 29999999999999999999

Offset: 1

Author

Lekraj Beedassy, Aug 02 2008

Keywords

• base
• nonn

Comments

k can never be 1, 4, or 7, because if it were, k*10^m - 1 would be divisible by 3.

Links

• Jon E. Schoenfield, Table of n, a(n) for n = 1..71 (next term is 8*10^1219 - 1)

Crossrefs

Cf. A055558, A065582.

Programs

Mathematica

d={9};s={};Do[Do[m=FromDigits[Join[IntegerDigits[i],d]];If[PrimeQ[m],AppendTo[s,m]],{i,8}];AppendTo[d,9],{j,19}];s (* James C. McMahon, Jul 20 2025 *)

Extensions

59999999 from Howard Berman (howard_berman(AT)hotmail.com), Apr 22 2009

Two more terms from Jon E. Schoenfield, Jan 12 2019