|
|
A100296
|
|
Sequence generated from a symmetric matrix.
|
|
2
|
|
|
1, 6, 25, 111, 488, 2149, 9461, 41654, 183389, 807403, 3554736, 15650361, 68903513, 303360038, 1335596817, 5880203831, 25888648920, 113979406525, 501814720109, 2209329044566, 9726966211957, 42824708216851, 188543436246752, 830096195208753, 3654646945111665
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
A100295 is generated from M^n * [1, 0, 0].
Limit_{n -> oo} a(n)/a(n-1) tends to 4.4026788295...a root of the characteristic polynomial of M, x^3 - 4*x^2 - 2*x + 1 and an eigenvalue of M.
|
|
LINKS
|
|
|
FORMULA
|
a(n) = rightmost term in M^n * [1,1,1], where M = [3,2,1; 2,1,0; 1,0,0].
a(n) = 4*a(n-1) + 2*a(n-2) - a(n-3).
G.f.: x*(1+2*x-x^2)/(1-4*x-2*x^2+x^3). - Colin Barker, May 25 2013
|
|
EXAMPLE
|
a(5) = 488 since M^5 * [1, 1, 1] = [2149, 1263, 488]. 2149 = a(6).
a(8) = 4*a(7) + 2*a(6) - a(5) =41654 = 4*9461 + 2*2149 - 488.
|
|
MAPLE
|
a:= n-> (<<3|2|1>, <2|1|0>, <1|0|0>>^n. <<1, 1, 1>>)[3, 1]:
|
|
MATHEMATICA
|
LinearRecurrence[{4, 2, -1}, {1, 6, 25}, 40] (* G. C. Greubel, Feb 05 2023 *)
|
|
PROG
|
(Magma) I:=[1, 6, 25]; [n le 3 select I[n] else 4*Self(n-1) +2*Self(n-2) -Self(n-3): n in [1..40]]; // G. C. Greubel, Feb 05 2023
(SageMath)
@CachedFunction
if (n<3): return (1, 1, 6)[n]
else: return 4*a(n-1) + 2*a(n-2) - a(n-3)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|