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 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 64 |
| 5 | 320 |
| 6 | 1568 |
| 7 | 7616 |
| 8 | 36864 |
| 9 | 178176 |
| 10 | 860672 |
| 11 | 4156416 |
| 12 | 20070400 |
| 13 | 96911360 |
| 14 | 467935232 |
| 15 | 2259402752 |
| 16 | 10909384704 |
| 17 | 52675215360 |
| 18 | 254338531328 |
| 19 | 1228055248896 |
| 20 | 5929575645184 |
| 21 | 28630524624896 |