A190310 Number of obtuse isosceles triangles, distinct up to congruence, on an n X n grid (or geoboard).

0, 0, 0, 1, 3, 5, 9, 12, 19, 24, 32, 37, 51, 57, 69, 80, 99, 107, 127, 136, 161, 176, 196, 207, 246, 262, 286, 306, 343, 357, 399, 414, 460, 485, 517, 544, 605, 623, 659, 689, 757

Offset: 1

Author

Martin Renner, May 08 2011

Keywords

• nonn

Links

• Eric Weisstein's World of Mathematics, Geoboard.
• Eric Weisstein's World of Mathematics, Obtuse Triangle.
• Eric Weisstein's World of Mathematics, Isosceles Triangle.

Crossrefs

Cf. A028419, A108279, A189978, A190022, A190309.

Formula

a(n) = A189978(n) - A190309(n) - A108279(n).