%I #13 Oct 14 2024 01:31:18

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

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

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

%C 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).

%C There is no further term up to 3000. Numbers corresponding to the larger terms are probable primes.

%C a(15) > 50000. - _Robert Price_, Oct 20 2014

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

%Y Cf. A072394, A178322.

%K nonn,hard,more

%O 1,2

%A _Farideh Firoozbakht_, May 26 2010

%E a(11)-a(14) from _Robert Price_, Oct 20 2014