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 A178321 Numbers n such that 58/111*(10^(3n)-1)-1 is prime. 2
 1, 2, 15, 74, 278, 541, 668, 1320, 1780, 1874, 4824, 13310, 20420, 24887 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If n is in the sequence then m=3*(58/111*(10^(3n)-1)-1)) is a term of A072394. Namely if n is a term of this sequence then for m=1/37*(58*10^(3n)-169) we have sigma(m)=reversal(m)-m (see comment lines of A072394). There is no further term up to 3000. Numbers corresponding to the larger terms are probable primes. a(15) > 50000. - Robert Price, Oct 20 2014 LINKS MATHEMATICA Do[If[PrimeQ[58/111*(10^(3 n) - 1) - 1], Print[n]], {n, 1874}] CROSSREFS Cf. A072394, A178322. Sequence in context: A056037 A125903 A268644 * A007232 A099743 A283842 Adjacent sequences:  A178318 A178319 A178320 * A178322 A178323 A178324 KEYWORD more,nonn AUTHOR Farideh Firoozbakht, May 26 2010 EXTENSIONS a(11)-a(14) from Robert Price, Oct 20 2014 STATUS approved

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Last modified October 21 10:29 EDT 2018. Contains 316414 sequences. (Running on oeis4.)