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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A118005 a(n) = ((-1)^n*5^(n+1) + 9^(n+1))/14. 0
1, 4, 61, 424, 4441, 36844, 347221, 3046864, 27812401, 248358484, 2244991981, 20156099704, 181649037961, 1633620638524, 14708689262341, 132347685782944, 1191281759937121, 10720772899980964, 96490770797094301 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Number of black cells after n iterations of Haferman's carpet.

LINKS

Table of n, a(n) for n=0..18.

Eric Weisstein's World of Mathematics, Haferman Carpet

Index entries for linear recurrences with constant coefficients, signature (4,45).

FORMULA

From Colin Barker, Jun 08 2013: (Start)

a(n) = 4*a(n-1) + 45*a(n-2).

G.f.: -1 / ((5*x+1)*(9*x-1)). (End)

CROSSREFS

Sequence in context: A158300 A129452 A131014 * A132064 A229666 A252973

Adjacent sequences:  A118002 A118003 A118004 * A118006 A118007 A118008

KEYWORD

nonn,easy

AUTHOR

Eric W. Weisstein, Apr 09 2006

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 May 21 22:24 EDT 2019. Contains 323467 sequences. (Running on oeis4.)