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 A138790 #22 May 08 2025 08:55:03
%S A138790 61,946
%N A138790 Numbers k such that A138793(k) is prime.
%C A138790 There are no more primes for k <= 5000.
%C A138790 a(3) > 20000. - _Robert Price_, Mar 24 2015
%e A138790 a(1) = 61 because the number 160695...654321 is prime.
%t A138790 b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[Reverse[a]]; If[PrimeQ[p], Print[n]; AppendTo[b, p]], {n, 1, 2000}]; b (* _Artur Jasinski_, Mar 30 2008 *)
%t A138790 Select[Range[1, 1000], PrimeQ[lst = {}; Do[lst = Join[lst, IntegerDigits[n]], {n, 1, #}]; FromDigits[Reverse[lst]]] &] (* _Robert Price_, Mar 24 2015 *)
%Y A138790 Cf. A000422, A116504, A007908, A116505, A138793.
%K A138790 nonn,bref,hard,more,base
%O A138790 1,1
%A A138790 _Artur Jasinski_, Mar 30 2008, Mar 31 2008