OFFSET
0,1
COMMENTS
a(n) gives the values of y satisfying 3*x^2 - y^2 = 363; corresponding x values are given by A296795.
a(n)/3 is the radius of the inscribed circle.
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
From Colin Barker, Dec 22 2017: (Start)
G.f.: 3*(4 + 5*x + 11*x^2 + 5*x^3 + 4*x^4) / (1 - 4*x^3 + x^6).
a(n) = 4*a(n-3) - a(n-6) for n>5.
(End)
EXAMPLE
If the sides are 17, 28, 39 the triangle has the altitude 15 against 28 and is a part of the Pythagorean triangle with the sides 15, 36, 39, so 15 is a term.
MATHEMATICA
CoefficientList[Series[3 (4 + 5 x + 11 x^2 + 5 x^3 + 4 x^4)/(1 - 4 x^3 + x^6), {x, 0, 35}], x] (* Michael De Vlieger, Dec 22 2017 *)
PROG
(PARI) Vec(3*(4 + 5*x + 11*x^2 + 5*x^3 + 4*x^4) / (1 - 4*x^3 + x^6) + O(x^40)) \\ Colin Barker, Dec 22 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Sture Sjöstedt, Dec 20 2017
EXTENSIONS
More terms from Colin Barker, Dec 22 2017
STATUS
approved