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A279415
Triangle read by rows: T(n,k), n>=k>=1, is the number of right isosceles triangles with integral coordinates that have a bounding box of size n X k.
8
0, 0, 4, 0, 2, 4, 0, 0, 4, 4, 0, 0, 2, 4, 4, 0, 0, 0, 4, 4, 4, 0, 0, 0, 2, 4, 4, 4, 0, 0, 0, 0, 4, 4, 4, 4, 0, 0, 0, 0, 2, 4, 4, 4, 4, 0, 0, 0, 0, 0, 4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 2, 4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 4, 4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 2, 4, 4
OFFSET
1,3
LINKS
Lars Blomberg, Table of n, a(n) for n = 1..9870 (the first 140 rows)
EXAMPLE
Triangle begins:
0
0,4
0,2,4
0,0,4,4
0,0,2,4,4
0,0,0,4,4,4
0,0,0,2,4,4,4
0,0,0,0,4,4,4,4
0,0,0,0,2,4,4,4,4
0,0,0,0,0,4,4,4,4,4
0,0,0,0,0,2,4,4,4,4,4
0,0,0,0,0,0,4,4,4,4,4,4
0,0,0,0,0,0,2,4,4,4,4,4,4
-------
The right angle is 'o'.
For n=4, k=3:
x... .o.. ..o. ...x
...x ...x x... x...
.o.. x... ...x ..o.
So T(4,3)=4
-------
For n=4, k=4:
o..x x..o x... ...x
.... .... .... ....
.... .... .... ....
x... ...x o..x x..o
So T(4,4)=4
CROSSREFS
Cf. A187452.
See A280639 for obtuse 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: A058997 A261164 A323982 * A201399 A145894 A366889
KEYWORD
nonn,tabl
AUTHOR
Lars Blomberg, Feb 27 2017
STATUS
approved