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 | 4 |
| 3 | 12 |
| 4 | 80 |
| 5 | 560 |
| 6 | 4512 |
| 7 | 40768 |
| 8 | 407808 |
| 9 | 4453632 |
| 10 | 52605440 |
| 11 | 667234304 |
| 12 | 9032423424 |
| 13 | 129822564352 |
| 14 | 1972450443264 |
| 15 | 31559866736640 |
| 16 | 530043925495808 |
| 17 | 9317136303718400 |
| 18 | 170976603113127936 |
| 19 | 3268020569256755200 |
| 20 | 64928967058257346560 |
| 21 | 1338431135849666052096 |