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A028987 Repdigit - 1 is prime (next term is 88...8 (72 digits)). 15
3, 4, 6, 8, 44, 444, 888, 2222, 8888, 444444, 888888, 444444444, 888888888, 444444444444, 888888888888, 222222222222222222, 444444444444444444444444444444, 44444444444444444444444444444444 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

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

P. 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: A063506 A084438 A186700 * A186709 A143037 A225059

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

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Last modified November 21 19:12 EST 2014. Contains 249784 sequences.