%I #15 May 27 2022 08:11:55

%S 1,3,3,29,3,3,19,3,3,457,3,3,16087,3,3,35963,3,3,167,3,3,7,3,3,13,3,3,

%T 953,3,3,7,3,3,548636579,3,3,19,3,3,71,3,3,13,3,3,89,3,3,114689,3,3,

%U 17,3,3,12037,3,3,7,3,3

%N a(1) = 1, a(n) = the smallest prime divisor of A138793(n).

%C a(61) > 10^11. - _Robert Price_, Mar 22 2015

%H Daniel Suteu, <a href="/A138962/b138962.txt">Table of n, a(n) for n = 1..333</a>

%F a(n) = A020639(A138793(n)). - _Daniel Suteu_, May 27 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[First[FactorInteger[p]]]], {n, 1, 31}]; b (* _Artur Jasinski_, Apr 04 2008 *)

%t lst = {}; Table[First[First[FactorInteger[FromDigits[Reverse[lst = Join[lst,IntegerDigits[n]]]]]]], {n, 1, 60}] (* _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) = my(k=f(n)); forprime(p=2, 10^6, if(k%p == 0, return(p))); if(n == 1, 1, vecmin(factor(k)[,1])); \\ _Daniel Suteu_, May 27 2022

%Y Cf. A020639, A138793, A104759, A000422, A116504, A007908, A116505, A104759, A075019, A075020, A075021, A075022, A138789, A138790, A138960, A138962.

%K nonn

%O 1,2

%A _Artur Jasinski_, Apr 04 2008

%E a(32)-a(60) from _Robert Price_, Mar 22 2015