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 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 96 |
| 6 | 576 |
| 7 | 3312 |
| 8 | 26496 |
| 9 | 198144 |
| 10 | 1691136 |
| 11 | 14973696 |
| 12 | 193370112 |
| 13 | 2034809856 |
| 14 | 25087186944 |
| 15 | 313539434496 |
| 16 | 4421478721536 |
| 17 | 58307347556352 |
| 18 | 915011420737536 |
| 19 | 13553664911437824 |
| 20 | 240637745416421376 |
| 21 | 3965015057937924096 |