A178321 Numbers k such that 58/111*(10^(3*k)-1)-1 is prime.

1, 2, 15, 74, 278, 541, 668, 1320, 1780, 1874, 4824, 13310, 20420, 24887

Offset: 1

Author

Farideh Firoozbakht, May 26 2010

Keywords

• nonn
• hard
• more

Comments

If k is in the sequence then m=3*(58/111*(10^(3*k)-1)-1) is a term of A072394.

Namely if k is a term of this sequence then for m=1/37*(58*10^(3*k)-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

Crossrefs

Cf. A072394, A178322.

Programs

Mathematica

Do[If[PrimeQ[58/111*(10^(3 n) - 1) - 1], Print[n]], {n, 1874}]

Extensions

a(11)-a(14) from Robert Price, Oct 20 2014