OFFSET
1,2
COMMENTS
The corresponding values of x are in A003499.
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 (6,-1).
FORMULA
G.f.: 48*x^2 / (1 - 6*x + x^2).
a(n) = 6*a(n-1) - a(n-2) for n>2.
a(n) = 48*A001109(n-1).
a(n) = 6*sqrt(2)*(-(3 - 2*sqrt(2))^n*(3+2*sqrt(2)) + (3 - 2*sqrt(2))*(3 + 2*sqrt(2))^n).
EXAMPLE
48 is in the sequence because (x, y) = (6,48) is a solution to y^2 = 72*x^2 - 288.
PROG
(PARI) concat(0, Vec(48*x^2 / (1 - 6*x + x^2) + O(x^25)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jan 18 2017
STATUS
approved