OFFSET
3,1
LINKS
Robert Israel, Table of n, a(n) for n = 3..851
Index entries for linear recurrences with constant coefficients, signature (24, -158, 360, -225).
FORMULA
a(n) = -1/14 - 5^n/10 + 3^n/6 + 15^n/210.
G.f.: 8*x^3/(225*x^4-360*x^3+158*x^2-24*x+1).
EXAMPLE
a(3) is the area of the triangle with vertices (1,1), (3,5) and (9,25), which is 8.
MAPLE
f:= n -> -1/14 - 5^n/10 + 3^n/6 + 15^n/210:
map(f, [$3..30]);
MATHEMATICA
Drop[CoefficientList[Series[8 x^3/(225 x^4 - 360 x^3 + 158 x^2 - 24 x + 1), {x, 0, 22}], x], 3] (* Michael De Vlieger, Dec 07 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Dec 07 2020
STATUS
approved