OFFSET
1,2
COMMENTS
The corresponding values of x are in A281241.
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
S. Vidhyalakshmi, V. Krithika, K. Agalya, On The Negative Pell Equation y^2 = 72*x^2 - 8, International Journal of Emerging Technologies in Engineering Research (IJETER), Volume 4, Issue 2, February (2016).
Index entries for linear recurrences with constant coefficients, signature (0,0,6,0,0,-1).
FORMULA
a(n) = 6*a(n-3) - a(n-6) for n>6.
G.f.: 192*x^2*(3 + 10*x + 17*x^2 + 10*x^3 + 3*x^4) / (1 - 6*x^3 + x^6).
EXAMPLE
576 is in the sequence because (x, y) = (152,576) is a solution to y^2 = 72*x^2 - 1331712.
MATHEMATICA
Rest@ CoefficientList[Series[192 x^2*(3 + 10 x + 17 x^2 + 10 x^3 + 3 x^4)/(1 - 6 x^3 + x^6), {x, 0, 29}], x] (* Michael De Vlieger, Jan 19 2017 *)
LinearRecurrence[{0, 0, 6, 0, 0, -1}, {0, 576, 1920, 3264, 5376, 12096}, 30] (* Harvey P. Dale, Feb 22 2018 *)
PROG
(PARI) concat(0, Vec(192*x^2*(3 + 10*x + 17*x^2 + 10*x^3 + 3*x^4) / (1 - 6*x^3 + x^6) + O(x^40)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jan 19 2017
STATUS
approved