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

0,1

Comments

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

Links

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

Mathematica

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

Crossrefs

Sequence in context: A020754 A052381 A219877 * A331038 A001566 A173771

Adjacent sequences: A031437 A031438 A031439 * A031441 A031442 A031443

Keyword

nonn,nice

Author

Yasutoshi Kohmoto

Extensions

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

Status

approved