login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A123744 Circulants of Fibonacci numbers (including F_0 = 0). 3
0, 1, 2, 16, 287, 16128, 2192140, 830952837, 805644641664, 2080690769701456, 14002804169885909807, 247753675148653634781184, 11469641168045182197979378136, 1391545878431673359565624090480585 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

A circulant C_n is the determinant of a circulant n X n matrix M, i.e. one with entries M_{i,j}=a_{i-j} where the indices are taken mod n. Hence C_n=C_n([a_n,a_{n-1},...,a_1]), with the first row of M given.

The eigenvalues of a circulant n X n matrix M(n) are lambda^{(n)}_k=sum(a_j*(rho_n)^(j*k),j=1..n), with the n-th roots of unity (rho_n)^k, k=1..n, where rho_n:=exp(2*Pi/n). See the P. J. Davis reference which uses a different convention.

REFERENCES

P. J. Davis, Circulant Matrices, J. Wiley, New York, 1979.

LINKS

Table of n, a(n) for n=1..14.

FORMULA

a(n)=product(lambda^{(n)}_k,k=1..n), with lambda^{(n)}_k=sum(F_{j-1}*(rho_n)^(j*k),j=1..n).

a(n) = C_n([F_{n-1},F_{n-2},...,F_0]) with the Fibonacci numbers F_n:=A000045(n) and the circulant C_n (see comment above).

EXAMPLE

n=4: the circular 4 X 4 matrix is M(4) = matrix([[2,1,1,0],[0,2,1,1],[1,0,2,1],[1,1,0,2]]).

n=4: 4th roots of unity: rho_4 = I, (rho_4)^2 = -1, (rho_4)^3 = -I, (rho_4)^4 =1, with I^2=-1. A123744 n=4: the eigenvalues of M(4) are therefore: 0*I^k + 1*(-1)^k + 1*(-I)^k + 2*1^k, k=1,...,4, namely 1-I, 2, 1+I, 4.

n=4: a(4)= Det(M(4)) = 16 = (1-I)*2*(1+I)*4.

CROSSREFS

Cf. A123745 (other Fibonacci circulants without F_0 = 0).

Sequence in context: A189257 A227674 A102599 * A136796 A055546 A009549

Adjacent sequences:  A123741 A123742 A123743 * A123745 A123746 A123747

KEYWORD

nonn,easy

AUTHOR

Wolfdieter Lang Nov 10 2006, Jan 27 2009

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 16 10:43 EDT 2018. Contains 316262 sequences. (Running on oeis4.)