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A206601 3^(n(n+1)/2) - 1. 0
0, 2, 26, 728, 59048, 14348906, 10460353202, 22876792454960, 150094635296999120, 2954312706550833698642, 174449211009120179071170506, 30903154382632612361920641803528, 16423203268260658146231467800709255288, 26183890704263137277674192438430182020124346 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
There are n cities located on the vertices of a convex n-gon 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 communication-line types is c, then a(n) = (c+1)^(n(n+1)/2)-1. Thus other sequences of this type can be generated.
LINKS
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
Sequence in context: A371296 A373869 A371297 * A156211 A156212 A138524
KEYWORD
easy,nonn
AUTHOR
Ivan N. Ianakiev, Feb 10 2012
STATUS
approved

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Last modified June 21 06:38 EDT 2024. Contains 373540 sequences. (Running on oeis4.)