|
|
A085504
|
|
Horadam sequence (0,1,9,3).
|
|
1
|
|
|
0, 1, 18, 81, 405, 1944, 9477, 45927, 223074, 1082565, 5255361, 25509168, 123825753, 601059771, 2917611090, 14162371209, 68745613437, 333698181192, 1619805064509, 7862698824255, 38166342053346, 185263315578333, 899287025215113, 4365230915850336
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
COMMENTS
|
Lim_{n->infinity} a(n)/a(n-1) = (3/2)*(1 + sqrt(5)), which can also be written as phi^2 + 2*phi - 1, phi^3 + phi - 1, phi + sqrt(5) + 1, 3*phi, 3*phi^2 - 3, phi^4 - 2 and lim_{n->infinity} (3/2)*(1 + Lucas(n)/Fibonacci(n)).
|
|
LINKS
|
|
|
FORMULA
|
a(n) = s*a(n-1) + r*a(n-2); for n > 3, where a(0) = 0, a(1) = 1, a(2) = 18, a(4) = 81, s = 3, r = 9.
G.f.: x*(1+15*x+18*x^2)/(1-3*x-9*x^2). [Colin Barker, Jun 20 2012]
|
|
EXAMPLE
|
a(4) = 405 because a(3) = 81, a(2) = 18, s = 3, r = 9 and (3 * 81) + (9 * 18) = 405.
|
|
MATHEMATICA
|
Join[{0, 1}, LinearRecurrence[{3, 9}, {18, 81}, 30]] (* or *) CoefficientList[ Series[x (1+15x+18x^2)/(1-3x-9x^2), {x, 0, 30}], x] (* Harvey P. Dale, Nov 24 2012 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
EXTENSIONS
|
First formula corrected and more terms from Harvey P. Dale, Nov 24 2012
|
|
STATUS
|
approved
|
|
|
|