A028987 Repdigit - 1 is prime.

3, 4, 6, 8, 44, 444, 888, 2222, 8888, 444444, 888888, 444444444, 888888888, 444444444444, 888888888888, 222222222222222222, 444444444444444444444444444444, 44444444444444444444444444444444

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Comments

Next term is 88...8 (72 digits).

Corresponding values of primes are in A096843. - Jaroslav Krizek, Mar 19 2013

Links

• Patrick De Geest, Repdigits : WONplate 83

Crossrefs

Cf. A010785.

Programs

Mathematica

a[n_]:=NestList[FromDigits[Append[{#},n]]&,n,35]; Union[Join[{3},Flatten[Table[Select[a[n],PrimeQ[#-1]&],{n,2,8,2}]]]] (* Jayanta Basu, May 29 2013 *)

PARI

u=30; for(n=1, u, r=(10^n-1)/9; for(a=1, 9, m=r*a; if(ispseudoprime(m-1), print1(m, ", ")))) \\ Felix Fröhlich, Jul 07 2014

Extensions

Offset corrected and initial term added by Arkadiusz Wesolowski, Aug 14 2011