%I #24 May 26 2022 09:52:25
%S 1,7,107,149,953,218107,402859,4877,379721,4349353,169373,182473,
%T 1940144339383,2184641,437064932281,5136696159619,67580875919190833,
%U 1156764458711,464994193118899,4617931439293,1277512103328491957510030561,8177269604099
%N a(1) = 1, a(n) = the largest prime divisor of A138793(n).
%C For the smallest prime divisors of A138793 see A138962.
%H Daniel Suteu and Robert Price, <a href="/A138963/b138963.txt">Table of n, a(n) for n = 1..63</a> (terms a(1)..a(45) from Robert Price)
%F a(n) = A006530(A138793(n)). - _Daniel Suteu_, May 26 2022
%t b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[Reverse[a]]; AppendTo[b, First[Last[FactorInteger[p]]]], {n, 1, 31}]; b (* _Artur Jasinski_, Apr 04 2008 *)
%t lst = {}; Table[First[Last[FactorInteger[FromDigits[Reverse[lst = Join[lst,IntegerDigits[n]]]]]]], {n, 1, 10}] (* _Robert Price_, Mar 22 2015 *)
%o (PARI)
%o f(n) = my(D = Vec(concat(apply(s->Str(s), [1..n])))); eval(concat(vector(#D, k, D[#D-k+1]))); \\ A138793
%o a(n) = if(n == 1, 1, vecmax(factor(f(n))[,1])); \\ _Daniel Suteu_, May 26 2022
%Y Cf. A006530, A138793, A138962.
%Y Cf. A104759, A000422, A116504, A007908, A116505, A104759, A075019, A075020, A075021, A075022, A138789, A138790, A138958, A138959, A138960.
%K nonn,base
%O 1,2
%A _Artur Jasinski_, Apr 04 2008