0,2

Together with A002320 these are the two sequences satisfying ( a(n)^2+a(n-1)^2 )/(1 - a(n)a(n-1)) is an integer, in both cases this integer is -5. - Floor van Lamoen (fvlamoen(AT)hotmail.com), Oct 26 2001

From a posting to Netnews group sci.math by ksbrown(AT)seanet.com (Kevin Brown) on Aug 15 1996.

Tanya Khovanova, Recursive Sequences

MathPages, N = (x^2 + y^2)/(1+xy) is a Square

Sequences A002310, A002320, and A049685 have this in common: each one satisfies a(n+1) = (a(n)^2+5)/a(n-1) - Graeme McRae (g_m(AT)mcraefamily.com), Jan 30 2005

Adjacent sequences: A002307 A002308 A002309 this_sequence A002311 A002312 A002313

Sequence in context: A132847 A121365 A018960 this_sequence A055728 A006795 A055824

nonn

Joe Keane (jgk(AT)jgk.org)