OFFSET
0,1
COMMENTS
a(n) gives values of x satisfying 3*x^2 - y^2 = 507; corresponding y values are given by A293846.
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (0,0,4,0,0,-1).
FORMULA
a(n) = 4*a(n-3)-a(n-6), a(1)= 13, a(2)= 14, a(3)= 19, a(4)= 26, a(5)= 37, a(6)= 62.
G.f.: (13 + 14*x + 19*x^2 - 26*x^3 - 19*x^4 - 14*x^5) / (1 - 4*x^3 + x^6). - Colin Barker, Dec 27 2017
EXAMPLE
The smallest triangle of this type with 3 acute angles has the sides: 61, 74, 87.
MATHEMATICA
LinearRecurrence[{0, 0, 4, 0, 0, -1}, {13, 14, 19, 26, 37, 62}, 40] (* Harvey P. Dale, Oct 10 2023 *)
PROG
(PARI) Vec((13 + 14*x + 19*x^2 - 26*x^3 - 19*x^4 - 14*x^5) / (1 - 4*x^3 + x^6) + O(x^40)) \\ Colin Barker, Dec 27 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Sture Sjöstedt, Dec 27 2017
STATUS
approved