A165978 Largest prime factor of number formed from a(n-1) with a 1 added at the end, a(1)=2.

2, 7, 71, 79, 113, 29, 97, 971, 83, 277, 163, 233, 37, 53, 59, 197, 73, 43, 431, 479, 1597, 15971, 383, 1277, 43, 431, 479, 1597, 15971, 383, 1277, 43, 431, 479, 1597, 15971, 383, 1277, 43, 431, 479, 1597, 15971, 383, 1277, 43, 431, 479, 1597, 15971, 383, 1277

Offset

1,1

Comments

Conjecture: The same number will never occur twice in this sequence. - Lowell

Disproved - cycle 43,431,479,1597,15971,383,1277 repeats starting at a(18). - Chandler

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

Largest prime factor of 21 is 7, so next term after 2 is 7.

Mathematica

NestList[FactorInteger[10#+1][[-1, 1]]&, 2, 60] (* Harvey P. Dale, Nov 10 2020 *)

Crossrefs

Sequence in context: A319640 A260566 A113866 * A106917 A188665 A198188

Adjacent sequences: A165975 A165976 A165977 * A165979 A165980 A165981

Keyword

base,nonn

Author

J. Lowell, Oct 02 2009

Extensions

Edited and extended by Ray Chandler, Nov 10 2009

Status

approved