

A206601


3^(n(n+1)/2)  1.


0



0, 2, 26, 728, 59048, 14348906, 10460353202, 22876792454960, 150094635296999120, 2954312706550833698642, 174449211009120179071170506, 30903154382632612361920641803528, 16423203268260658146231467800709255288, 26183890704263137277674192438430182020124346
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OFFSET

0,2


COMMENTS

There are n cities located on the vertices of a convex ngon and 2 types of communication lines available. Any city can be connected to any other by only one communication line (that can be of any type). A network exists if at least 2 cities are connected by a communication line. The sequence shows how many different networks a(n) can be built. In general, if the number of communicationline types is c, then a(n) = (c+1)^(n(n+1)/2)1. Thus other sequences of this type can be generated.


LINKS

Table of n, a(n) for n=0..13.


FORMULA

a(n) = (3^A000217)  1.
a(n) = A047656(n+1)  1.  Omar E. Pol, Feb 18 2012


EXAMPLE

In the case of 2 different types of communication lines and 4 cities, the number of different networks (connecting at least 2 cities) is 728.


CROSSREFS

Cf. A000217, A126883.
Sequence in context: A255538 A302719 A090247 * A156211 A156212 A138524
Adjacent sequences: A206598 A206599 A206600 * A206602 A206603 A206604


KEYWORD

easy,nonn


AUTHOR

Ivan N. Ianakiev, Feb 10 2012


STATUS

approved



