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A189415 Number of trapezoids on a (n X n)-grid (or geoboard). 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

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

Weisstein, Eric W.: MathWorld -- Trapezoid.

Nathaniel Johnston, C program for computing terms

CROSSREFS

Cf. 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

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Last modified November 14 23:25 EST 2018. Contains 317221 sequences. (Running on oeis4.)