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 A138960 #18 May 26 2022 09:52:20
%S A138960 1,2,3,2,3,2,127,2,3,857,3,3,18503,3,3,43,3,3,17,2,2,2,2,2,2,2,2,2,2,
%T A138960 3,7,3,3,1051,3,3,67103,3,3,2,2,2,2,2,2,2,2,2,2,3,3,5,3,3,5,3,3,5,3,2,
%U A138960 2,2,2,2,2,2,2,2,2
%N A138960 a(n) = smallest prime divisor of A138957(n).
%C A138960 For largest prime divisors see A138961.
%t A138960 a = {}; b = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[Length[w] - k + 1]]], {k, 1, Length[w]}]; p = FromDigits[a]; AppendTo[b, First[First[FactorInteger[p]]]], {n, 1, 38}]; b
%t A138960 A137957[n_] := FromDigits[Flatten[Reverse /@ IntegerDigits[Range[n]]]];
%t A138960 Table[FactorInteger[A137957[n]][[1, 1]], {n, 39}] (* _Robert Price_, May 10 2019 *)
%Y A138960 Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138961.
%K A138960 nonn,base
%O A138960 1,2
%A A138960 _Artur Jasinski_, Apr 04 2008
%E A138960 a(39)-a(69) from _Robert Price_, May 10 2019