A190317 - OEIS

A190317

Number of acute isosceles triangles on an n X n grid.

0, 0, 8, 48, 164, 448, 976, 1864, 3328, 5512, 8640, 12984, 18836, 26576, 36584, 49056, 64560, 83640, 106904, 134816, 168004, 206952, 252480, 305360, 366312, 436120, 515864, 605928, 707644, 822120, 950216, 1092784, 1251784, 1427848, 1622416, 1835968, 2070404

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

COMMENTS

Place all bounding boxes of A279418 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) * A279418(i,j))) where k=1 when i=j and k=2 otherwise. - Lars Blomberg, Mar 02 2017

LINKS

Lars Blomberg, Table of n, a(n) for n = 1..10000 (the first 100 terms from Chai Wah Wu)

FORMULA

a(n) = A186434(n) - A187452(n) - A190318(n).

CROSSREFS

Cf. A186434, A187452, A190318, A279418.

Sequence in context: A035471 A209443 A072819 * A073912 A212571 A247727

Adjacent sequences: A190314 A190315 A190316 * A190318 A190319 A190320

KEYWORD

nonn

AUTHOR

Martin Renner, May 08 2011

EXTENSIONS

a(10)-a(37) from Nathaniel Johnston, May 09 2011

STATUS

approved