OFFSET
1,1
COMMENTS
The corresponding values of y are in A281242.
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.: 8*x*(17 + 19*x + 33*x^2 - 51*x^3 - 33*x^4 - 19*x^5) / (1 - 6*x^3 + x^6).
EXAMPLE
152 is in the sequence because (x, y) = (152,576) is a solution to y^2 = 72*x^2 - 1331712.
MATHEMATICA
Rest@ CoefficientList[Series[8 x (17 + 19 x + 33 x^2 - 51 x^3 - 33 x^4 - 19 x^5)/(1 - 6 x^3 + x^6), {x, 0, 31}], x] (* Michael De Vlieger, Jan 19 2017 *)
PROG
(PARI) Vec(8*x*(17 + 19*x + 33*x^2 - 51*x^3 - 33*x^4 - 19*x^5) / (1 - 6*x^3 + x^6) + O(x^40))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jan 19 2017
STATUS
approved