OFFSET
1,1
COMMENTS
The corresponding values of y are given by a(n+2).
Positive values of x (or y) satisfying x^2 - 14xy + y^2 + 176 = 0.
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (0,4,0,-1).
FORMULA
a(n) = 4*a(n-2)-a(n-4).
G.f.: -x*(x-1)*(x+2)*(2*x+1) / (x^4-4*x^2+1).
EXAMPLE
10 is in the sequence because (x, y) = (10, 37) is a solution to x^2 - 4xy + y^2 + 11 = 0.
PROG
(PARI) Vec(-x*(x-1)*(x+2)*(2*x+1)/(x^4-4*x^2+1) + O(x^100))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Feb 05 2014
STATUS
approved