A190839 a(n) is the greatest prime divisor of 10^(2*n)+10^n+1.

37, 37, 333667, 9901, 2906161, 333667, 10838689, 99990001, 440334654777631, 2906161, 1344628210313298373, 999999000001, 900900900900990990990991, 10838689, 4185502830133110721, 9999999900000001, 13168164561429877, 440334654777631, 3931123022305129377976519, 39526741

Offset: 1

Author

Vladimir Shevelev, May 21 2011

Keywords

• nonn
• base

Comments

(10^(2*n)+10^n+1)^3 is palindrome.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..158
• factordb, 10^(2*n)+10^n+1.

Crossrefs

Cf. A002780, A006530, A066138.

Programs

Mathematica

f[n_]:=Max[Transpose[FactorInteger[10^(2n)+10^n+1]][[1]]]; Array[f,20] (* Harvey P. Dale, Jun 10 2011 *)

PARI

u(n)=10^(2*n)+10^n+1; for(n=1,30,f=factor(u(n));print1(f[matsize(f)[1],1],", ")) \\ Joerg Arndt, May 27 2011

Formula

a(n) = A006530(A066138(n)). - R. J. Mathar, Oct 30 2015