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

Author

Artur Jasinski, Apr 04 2008

Keywords

• nonn
• base

Comments

For smallest prime divisors see A138960.

Links

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

Crossrefs

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

Programs

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 *)