login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A099176 a(n)=2a(n-1)+4a(n-2)-4a(n-3)-4a(n-4). 2
1, 1, 4, 8, 24, 60, 168, 448, 1232, 3344, 9152, 24960, 68224, 186304, 509056, 1390592, 3799296, 10379520, 28357632, 77473792, 211662848, 578272256, 1579870208, 4316282880, 11792306176, 32217174016, 88018960384, 240472260608 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Form the 6 node graph with matrix A=[1,1,1,1,0,0; 1,1,0,0,1,1; 1,0,0,0,0,0; 1,0,0,0,0,0; 0,1,0,0,0,0; 0,1,0,0,0,0]. Then A099176 counts closed walks of length n at either of the degree 5 vertices.

LINKS

Table of n, a(n) for n=0..27.

Index entries for linear recurrences with constant coefficients, signature (2,4,-4,-4).

FORMULA

G.f.: (1+x)*(1-2*x)/((1-2x^2)(1-2x-2x^2)).

a(n)=(3+sqrt(3))(1+sqrt(3))^n/12+(3-sqrt(3))(1-sqrt(3))^n/12+2^((n-4)/2)(1+(-1)^n) a(n)=A002605(n)/2+2^((n-4)/2)(1+(-1)^n).

CROSSREFS

Cf. A099177.

Sequence in context: A332871 A116719 A159612 * A190156 A291024 A116556

Adjacent sequences:  A099173 A099174 A099175 * A099177 A099178 A099179

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Oct 02 2004

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 07:59 EDT 2020. Contains 333079 sequences. (Running on oeis4.)