A138961 a(n) = largest prime divisor of A138957(n).

1, 3, 41, 617, 823, 643, 9721, 14593, 3803, 14405693, 10939223, 4156374407, 2663693, 5603770631, 1221751714624799, 287108811653770498027, 74103167823547, 11843077531813991, 726216405947772436185983423, 769725127, 18274551225153265813469

Offset

1,2

Comments

For smallest prime divisors see A138960.

Links

Robert Price, Table of n, a(n) for n = 1..60

Mathematica

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[Last[FactorInteger[p]]]], {n, 1, 18}]; b
A137957[n_] := FromDigits[Flatten[Reverse /@ IntegerDigits[Range[n]]]];
Table[First[Last[FactorInteger[A137957[n]]]], {n, 39}] (* Robert Price, May 10 2019 *)

Crossrefs

Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138960.

Sequence in context: A189356 A155672 A073844 * A075022 A367981 A300281

Adjacent sequences: A138958 A138959 A138960 * A138962 A138963 A138964

Keyword

nonn,base

Author

Artur Jasinski, Apr 04 2008

Status

approved