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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

Table of n, a(n) for n=1..14.

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.)