A028987 Repdigit - 1 is prime.

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

Offset

1,1

Comments

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

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

Links

Table of n, a(n) for n=1..18.

Patrick De Geest, Repdigits : WONplate 83

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 *)

Prog

(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

Crossrefs

Cf. A010785.

Sequence in context: A084438 A186700 A350217 * A284615 A186709 A143037

Adjacent sequences: A028984 A028985 A028986 * A028988 A028989 A028990

Keyword

nonn,base

Author

Patrick De Geest

Extensions

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

Status

approved