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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A243213 Number of ways to place 4 points on a triangular grid of side length n so that no three of them are vertices of an equilateral triangle with sides parallel to the grid.

Table of values

n a(n)
3 3
4 128
5 1062
6 5160
7 18591
8 55113
9 142005
10 329045
11 701160
12 1395975
13 2626953
14 4713723
15 8120322
16 13503350
17 21770766
18 34153758
19 52292385
20 78337890
21 115072320
22 166048850
23 235753353
24 329791143
25 455099307
26 620189115
27 835418766
28 1113301553
29 1468849515
30 1919958285

List of values

[3, 128, 1062, 5160, 18591, 55113, 142005, 329045, 701160, 1395975, 2626953, 4713723, 8120322, 13503350, 21770766, 34153758, 52292385, 78337890, 115072320, 166048850, 235753353, 329791143, 455099307, 620189115, 835418766, 1113301553, 1468849515, 1919958285]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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