A031440 a(0) = 3; for n > 0, a(n) is the greatest prime factor of a(n-1)^2 - 2.

3, 7, 47, 2207, 4481, 26111, 189017, 67271, 11815633, 606737, 708641, 354023, 125332284527, 51939720282500417, 18062107820423, 1376080289340623571113, 4012316132900773615751, 983669740542169, 4443427285129103, 19744046038229790810567377584607, 4300749014896245437702886338812998834884967953, 41572359968343362282287450730112204489086145685200294134959430572332688727999

Offset: 0

Author

Yasutoshi Kohmoto

Keywords

• nonn
• nice

Comments

Is this sequence unbounded? [Charles R Greathouse IV, Dec 29 2011]

Links

• Dennis Langdeau, Table of n, a(n) for n = 0..23

Programs

Mathematica

NestList[FactorInteger[#^2-2][[-1,1]]&,3,22] (* Harvey P. Dale, Jan 10 2013 *)

Extensions

More terms from Dennis Langdeau (dlangdea(AT)sfu.ca), Jun 26 2006