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A190318 Number of obtuse isosceles triangles on a (n X n)-grid. 4


%S 0,0,0,4,36,100,256,496,968,1672,2736,4092,6188,8764,12144,16464,

%T 22224,28928,37400,47076,59244,73580,90344,109000,132048,158000,

%U 187528,220716,259348,301388,350088,402792,463176,529720,602888,683092,774476,872100,978232

%N Number of obtuse isosceles triangles on a (n X n)-grid.

%C Place all bounding boxes of A280639 that will fit into the n X n grid in all possible positions, and the proper rectangles in two orientations: a(n) = Sum(i=1..n, Sum(j=1..i, k * (n-i+1) * (n-j+1) * A280639(i,j))) where k=1 when i=j and k=2 otherwise. - _Lars Blomberg_, Mar 02 2017

%H Lars Blomberg, <a href="/A190318/b190318.txt">Table of n, a(n) for n = 1..10000</a> (the first 100 terms from Chai Wah Wu)

%H Nathaniel Johnston, <a href="/A190318/a190318.c.txt">C program for computing terms</a>

%F a(n) = A186434(n) - A190317(n) - A187452(n).

%Y Cf. A186434, A187452, A190317, A280639.

%K nonn

%O 1,4

%A _Martin Renner_, May 08 2011

%E a(10)-a(39) from _Nathaniel Johnston_, May 09 2011

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Last modified November 20 02:34 EST 2019. Contains 329323 sequences. (Running on oeis4.)