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A119633 (A046717(n))^3. 1
1, 125, 2197, 68921, 1771561, 48627125, 1305751357, 35319837041, 953054410321, 25737699078125, 694870802988517, 18761935323400361, 506568440928284281, 13677382220238009125, 369289011109685057677, 9970806079491650694881 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

COMMENTS

Squareroot of M1 = A, the 8x8 matrix with the cyclotomic third roots of unity, mapped in a Gray code format. The 3 cyclotomic third roots of unity are (u, 1/u and 1), where u = (-.5 + (sqrt(3)/2)i), = (1 Angle 120 deg.); and 1/u = (-.5, -(sqrt(3)/2)i), = (1 Angle -120 deg.). Third root = 1. Thus A^2 = M1. A =

[1, u, 1/u, u, 1/u, 1, 1/u, u;

u, 1, u, 1/u, 1, 1/u, u, 1/u;

1/u, u, 1, u, 1/u, u, 1/u, 1;

u, 1/u, u, 1, u, 1/u, 1, 1/u;

1/u, 1, 1/u, u, 1, u, 1/u, u;

1, 1/u, u, 1/u, u, 1, u, 1/u;

1/u, u, 1/u, 1, 1/u, u, 1, u;

u, 1/u, 1, 1/u, u, 1/u, u, 1]

A046717 can be generated from the analogous 2 X 2 matrix: P = [ -1,2; 2,-1 ], (which has the square root, [ u,1/u; 1/u;u ]). Then left term of P^n * [ 1,0 ], (unsigned) = 1, 5, 13, 41, 121...(where A046717 begins 1, 1, 5, 13...).

Pascal's triangle squared: (1; 2,1; 4,4,1; 8,12,6,1;...) rows can be generated by taking the dot product of the distinct terms (...4, 2, 1) in rows or columns of the analogous "M" matrices and their frequency: e.g. row 1 of the 8x8 matrix (unsigned) = [1, 2, 4, 2, 4, 8, 4, 2] with a frequency for (8, 4, 2, 1) being (1, 3, 3, 1). Dot product = the (8, 12, 6, 1) row of Pascal's Triangle squared.

Third powers of A046717: (deleting the first "1": (1, 5, 13, 41, 121, 365...)).

Leftmost term (unsigned) of M1^n * [1,0,0,0,0,0,0,0]; where M1 = 8x8 matrix:

[ -1, 2, -4, 2, -4, 8, -4, 2;

2, -1, 2, -4, 8, -4, 2, -4;

-4, 2, -1, 2, -4, 2, -4, 8;

2, -4, 2, -1, 2, -4, 8, -4;

-4, 8, -4, 2, -1, 2, -4, 2;

8, -4, 2, -4, 2, -1, 2, -4;

-4, 2, -4, 8, -4, 2, -1, 2;

2, -4, 8, -4, 2, -4, 2, -1]

LINKS

Index to sequences with linear recurrences with constant coefficients, signature (20,210,-540,-729).

FORMULA

G.f.: x(1+105x-513x^2-729x^3)/((1+9x)(1-3x)(1-27x)(1+x)). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 09 2008]

EXAMPLE

a(3) = 2197 = 13^3 = (A046717(a))^3.

a(4) = 68921 = 41^3 = leftmost term of M1^n * [1,0,0,0,0,0,0,0].

CROSSREFS

Cf. A046717, A120096.

Sequence in context: A102061 A080169 A017127 * A017223 A017331 A030690

Adjacent sequences:  A119630 A119631 A119632 * A119634 A119635 A119636

KEYWORD

nonn,easy,uned

AUTHOR

Gary W. Adamson (qntmpkt(AT)yahoo.com), Jun 09 2006

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Last modified February 15 12:25 EST 2012. Contains 205786 sequences.