A138963 a(1) = 1, a(n) = the largest prime divisor of A138793(n).

1, 7, 107, 149, 953, 218107, 402859, 4877, 379721, 4349353, 169373, 182473, 1940144339383, 2184641, 437064932281, 5136696159619, 67580875919190833, 1156764458711, 464994193118899, 4617931439293, 1277512103328491957510030561, 8177269604099

Offset

1,2

Comments

For the smallest prime divisors of A138793 see A138962.

Links

Daniel Suteu and Robert Price, Table of n, a(n) for n = 1..63 (terms a(1)..a(45) from Robert Price)

Formula

a(n) = A006530(A138793(n)). - Daniel Suteu, May 26 2022

Mathematica

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 *)
lst = {}; Table[First[Last[FactorInteger[FromDigits[Reverse[lst = Join[lst, IntegerDigits[n]]]]]]], {n, 1, 10}] (* Robert Price, Mar 22 2015 *)

Prog

(PARI)
f(n) = my(D = Vec(concat(apply(s->Str(s), [1..n])))); eval(concat(vector(#D, k, D[#D-k+1]))); \\ A138793
a(n) = if(n == 1, 1, vecmax(factor(f(n))[, 1])); \\ Daniel Suteu, May 26 2022

Crossrefs

Cf. A006530, A138793, A138962.

Cf. A104759, A000422, A116504, A007908, A116505, A104759, A075019, A075020, A075021, A075022, A138789, A138790, A138958, A138959, A138960.

Sequence in context: A231899 A188407 A075021 * A141932 A002687 A354572

Adjacent sequences: A138960 A138961 A138962 * A138964 A138965 A138966

Keyword

nonn,base

Author

Artur Jasinski, Apr 04 2008

Status

approved