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A028987
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Repdigit - 1 is prime (next term is 88...8 (72 digits)).
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15
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3, 4, 6, 8, 44, 444, 888, 2222, 8888, 444444, 888888, 444444444, 888888888, 444444444444, 888888888888, 222222222222222222, 444444444444444444444444444444, 44444444444444444444444444444444
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OFFSET
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1,1
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COMMENTS
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Corresponding values of primes are in A096843. - Jaroslav Krizek, Mar 19 2013.
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LINKS
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Table of n, a(n) for n=1..18.
P. De Geest, Repdigits : WONplate 83
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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Cf. A010785.
Sequence in context: A063506 A084438 A186700 * A284615 A186709 A143037
Adjacent sequences: A028984 A028985 A028986 * A028988 A028989 A028990
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KEYWORD
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nonn,base
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AUTHOR
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Patrick De Geest
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EXTENSIONS
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Offset corrected and initial term added by Arkadiusz Wesolowski, Aug 14 2011
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STATUS
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approved
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