login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A128650 Number of polygons on n vertices with exactly three faces. 4
0, 4, 16, 60, 224, 840, 3168, 12012, 45760, 175032, 671840, 2586584, 9984576, 38630800, 149768640, 581690700, 2262890880, 8815845720, 34389986400, 134312002440, 525129633600, 2055166429680, 8050465600320, 31561484455800 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,2
LINKS
T. Mansour and S. Severini, Grid polygons from permutations and their enumeration by the kernel method, arXiv:math/0603225 [math.CO], 2006.
FORMULA
a(n) = 4*(n-2)/(n-1) * C(2*n-4,n-2).
For n>2, a(n) = 4*A001791(n-2).
MATHEMATICA
Table[4 Binomial[2n-4, n-3], {n, 2, 25}] (* Jean-François Alcover, Dec 05 2018 *)
CROSSREFS
Sequence in context: A269532 A269673 A231896 * A072335 A081161 A032106
KEYWORD
nonn
AUTHOR
Ralf Stephan, May 08 2007
STATUS
approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 22 00:43 EST 2024. Contains 370239 sequences. (Running on oeis4.)