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Consider the figure made up of a row of n adjacent congruent rectangles, with diagonals of all possible rectangles drawn; a(n) = number of interior vertices where exactly three lines cross.
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%I #8 Jul 25 2020 14:00:39

%S 0,1,2,8,18,32,50,102,126,198,286,390,510,742,878,1130,1414,1770,2166,

%T 2778,3186,3858,4594,5342,6146,7342,8294,9662,11134,12710,14390,16582,

%U 18226,20518,22946,25662,28530,32270,35250,38862,42650,46614,50754,55990,60730

%N Consider the figure made up of a row of n adjacent congruent rectangles, with diagonals of all possible rectangles drawn; a(n) = number of interior vertices where exactly three lines cross.

%H Lars Blomberg, <a href="/A336489/b336489.txt">Table of n, a(n) for n = 1..500</a>

%Y Cf. A334701, A336490, A336491.

%K nonn

%O 1,3

%A _Lars Blomberg_, Jul 25 2020