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!)
A328890 Number of acyclic edge covers of the complete bipartite graph K_{n,2}. 2
1, 6, 18, 46, 110, 254, 574, 1278, 2814, 6142, 13310, 28670, 61438, 131070, 278526, 589822, 1245182, 2621438, 5505022, 11534334, 24117246, 50331646, 104857598, 218103806, 452984830, 939524094, 1946157054, 4026531838, 8321499134, 17179869182, 35433480190, 73014444030 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Complete Bipartite Graph
FORMULA
a(n) = 2*A000225(n-1) + A001787(n).
a(n) = (2 + n)*2^(n-1) - 2.
From Colin Barker, Nov 05 2019: (Start)
G.f.: x*(1 + x - 4*x^2) / ((1 - x)*(1 - 2*x)^2).
a(n) = 5*a(n-1) - 8*a(n-2) + 4*a(n-3) for n>3.
(End)
PROG
(PARI) a(n) = {(2 + n)*2^(n-1) - 2}
(PARI) Vec(x*(1 + x - 4*x^2) / ((1 - x)*(1 - 2*x)^2) + O(x^30)) \\ Colin Barker, Nov 05 2019
CROSSREFS
Column 2 of A328888.
Sequence in context: A031128 A304161 A261016 * A188379 A299268 A248462
KEYWORD
nonn,easy
AUTHOR
Andrew Howroyd, Oct 29 2019
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 April 21 11:17 EDT 2024. Contains 371853 sequences. (Running on oeis4.)