A189415 Number of trapezoids on an n X n grid (or geoboard).

0, 1, 50, 490, 2618, 9519, 28432, 70796, 157912, 321161, 610482, 1082570, 1848362, 3003015, 4716792, 7204604, 10730528, 15530189, 22093410, 30723078, 42146178, 56981411, 75952240, 99685104, 129757248

Offset

1,3

Links

Table of n, a(n) for n=1..25.

Eric Weisstein's World of Mathematics, Trapezoid.

Nathaniel Johnston, C program for computing terms.

Crossrefs

Cf. A181945, A186434, A189413, A189414, A189416, A189418.

Sequence in context: A228743 A019561 A164757 * A128954 A022147 A285044

Adjacent sequences: A189412 A189413 A189414 * A189416 A189417 A189418

Keyword

nonn

Author

Martin Renner, Apr 21 2011

Extensions

a(6)-a(25) from Nathaniel Johnston, Apr 25 2011

Status

approved