OFFSET
0,2
COMMENTS
-3*a(n)^2 + b(n)^2 = 13, with the companion sequence b(n)= A077238(n).
LINKS
Matthew House, Table of n, a(n) for n = 0..3478
Index entries for linear recurrences with constant coefficients, signature (0,4,0,-1).
FORMULA
G.f.: (1+x)*(1+x+x^2)/(1-4*x^2+x^4).
a(n) = 4*a(n-2) - a(n-4). - Matthew House, Feb 11 2017
EXAMPLE
3*a(2)^2 + 13 = 3*36+13 = 121 = 11^2 = A077238(2)^2.
MATHEMATICA
CoefficientList[Series[(1 + x) (1 + x + x^2)/(1 - 4 x^2 + x^4), {x, 0, 28}], x] (* Michael De Vlieger, Feb 11 2017 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Nov 08 2002
STATUS
approved