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.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | -2 |
| 4 | -6 |
| 5 | -18 |
| 6 | -54 |
| 7 | -168 |
| 8 | -534 |
| 9 | -1732 |
| 10 | -5706 |
| 11 | -19038 |
| 12 | -64176 |
| 13 | -218190 |
| 14 | -747180 |
| 15 | -2574488 |
| 16 | -8918070 |
| 17 | -31036560 |
| 18 | -108457488 |
| 19 | -380390574 |
| 20 | -1338495492 |
| 21 | -4723664566 |
| 22 | -16714545822 |
| 23 | -59286878556 |
| 24 | -210755970528 |
| 25 | -750721297056 |
| 26 | -2679075662922 |
| 27 | -9577156141654 |
| 28 | -34290858526926 |
| 29 | -122959225609518 |