This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A178321 #13 Oct 14 2024 01:31:18
%S A178321 1,2,15,74,278,541,668,1320,1780,1874,4824,13310,20420,24887
%N A178321 Numbers k such that 58/111*(10^(3*k)-1)-1 is prime.
%C A178321 If k is in the sequence then m=3*(58/111*(10^(3*k)-1)-1) is a term of A072394.
%C A178321 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 A178321 There is no further term up to 3000. Numbers corresponding to the larger terms are probable primes.
%C A178321 a(15) > 50000. - _Robert Price_, Oct 20 2014
%t A178321 Do[If[PrimeQ[58/111*(10^(3 n) - 1) - 1], Print[n]], {n, 1874}]
%Y A178321 Cf. A072394, A178322.
%K A178321 nonn,hard,more
%O A178321 1,2
%A A178321 _Farideh Firoozbakht_, May 26 2010
%E A178321 a(11)-a(14) from _Robert Price_, Oct 20 2014