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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 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

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Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)