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A280639
Triangle read by rows: T(n,k), n>=k>=1, is the number of obtuse isosceles triangles with integral coordinates that have a bounding box of size n X k.
9
0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 2, 0, 0, 4, 0, 0, 0, 0, 0, 8, 0, 2, 2, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 12, 0, 2, 2, 2, 4, 0, 0, 0, 12, 0, 0, 0, 4, 0, 0, 0, 0, 0, 16, 0, 2, 2, 2, 2, 0, 0, 0, 0, 0, 16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 20, 0, 2, 2, 2, 2, 6, 4
OFFSET
1,10
LINKS
Lars Blomberg, Table of n, a(n) for n = 1..9870 (the first 140 rows)
EXAMPLE
Triangle begins:
0
0,0
0,0,0
0,0,0,4
0,2,0,0,4
0,0,0,0,0,8
0,2,2,0,0,0,8
0,0,0,0,0,0,0,12
0,2,2,2,4,0,0,0,12
0,0,0,4,0,0,0,0,0,16
0,2,2,2,2,0,0,0,0,0,16
0,0,0,0,0,0,0,0,0,0,0,20
0,2,2,2,2,6,4,4,4,0,0,0,20
-------
The obtuse angle is 'o'.
For n=4, k=4:
x... x... ...x ...x
..o. .... .o.. ....
.... .o.. .... ..o.
...x ...x x... x...
So T(4,4)=4
-------
For n=5, k=2:
x...x ..o..
..o.. x...x
So T(5,2)=2
CROSSREFS
Cf. A190318.
See A279415 for right isosceles triangles.
See A279418 for acute isosceles triangles.
See A279413 for all isosceles triangles.
See A279433 for all right triangles.
See A280652 for all obtuse triangles.
See A280653 for all acute triangles.
See A279432 for all triangles.
Sequence in context: A355997 A136452 A247703 * A350708 A319037 A067565
KEYWORD
nonn,tabl
AUTHOR
Lars Blomberg, Feb 27 2017
STATUS
approved