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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) is the number of interior vertices where exactly four lines cross.
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%I #14 Oct 01 2020 04:04:47

%S 0,0,1,2,2,10,22,18,32,62,100,118,136,154,274,346,426,554,698,726,884,

%T 1058,1248,1454,1784,2146,2714,2978,3250,3722,4226,4490,5104,5758,

%U 6674,7350,8058,8798,10062,11238,12478,14046,15702,16526,18016,19570,21188,22870

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

%H Lars Blomberg, <a href="/A336490/b336490.txt">Table of n, a(n) for n = 1..500</a>

%Y Cf. A334701, A336489, A336491.

%K nonn

%O 1,4

%A _Lars Blomberg_, Jul 25 2020