4,1

The n X n circulant matrix used here has first row 1 through n and each successive row is a circular rotation of the previous row to the right by one element.

The coefficient of x^(n-4) exists only for n>3, so the sequence starts with a(4). In order to obtain a nonnegative sequence the coefficient (which is negative for all n>3) is multiplied by -1.

Daniel Zwillinger, ed., "CRC Standard Mathematical Tables and Formulae", 31st Edition, ISBN 1-58488-291, Section 2.6.2.25 (page 141) and Section 2.6.11.3 (page 152).

a(n+3) = n*(n+1)*(n+2)*(n+3)^4*(3*n+22)/(2*5!) for n>=1.

a(n) = (3*n^8-5*n^7-45*n^6+125*n^5-78*n^4)/(2*5!) for n>=4.

The circulant matrix for n = 5 is

[1 2 3 4 5]

[5 1 2 3 4]

[4 5 1 2 3]

[3 4 5 1 2]

[2 3 4 5 1]

The characteristic polynomial of this matrix is x^5 - 5*x^4 -100*x^3 - 625*x^2 - 1750*x - 1875. The coeffient of x^(n-4) is -1750, hence a(5) = 1750.

(OCTAVE, MATLAB) n * (n+1) * (n+2) * (n+3)^4 * (3*n + 22) / (2 * factorial(5)); - Paul M. Payton, Jan 14 2007

(MAGMA) 1. [ -Coefficient(CharacteristicPolynomial(Matrix(IntegerRing(), n, n, [< i, j, 1 + (j-i) mod n > : i, j in [1..n] ] )), n-4) : n in [4..26] ] ; 2. [ (n-3)*(n-2)*(n-1)*n^4*(3*n+13) / (2 * Factorial(5)) : n in [4..26] ] ; - Klaus Brockhaus, Jan 27 2007

(PARI) 1. {for(n=4, 26, print1(-polcoeff(charpoly(matrix(n, n, i, j, (j-i)%n+1), x), n-4), ", "))} 2. {for(n=4, 26, print1((3*n^8 - 5*n^7 - 45*n^6 + 125*n^5 - 78*n^4)/(2*5!), ", "))} - Klaus Brockhaus, Jan 27 2007

Cf. A000142 (factorial numbers), A014206 (n^2+n+2), A127407, A127408, A127410, A127411, A127412.

Sequence in context: A138854 A133530 A120103 this_sequence A013447 A013446 A013444

Adjacent sequences: A127406 A127407 A127408 this_sequence A127410 A127411 A127412

nonn,easy

Paul M. Payton (paul.payton(AT)lmco.com), Jan 14 2007

Edited, corrected and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Jan 27 2007