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 | 0 |
| 4 | 24 |
| 5 | 240 |
| 6 | 1560 |
| 7 | 8400 |
| 8 | 60984 |
| 9 | 912240 |
| 10 | 15938520 |
| 11 | 242998800 |
| 12 | 3300493944 |
| 13 | 44583979440 |
| 14 | 690641504280 |
| 15 | 12868117189200 |
| 16 | 264164524958904 |
| 17 | 5481631005177840 |
| 18 | 112822632387018840 |
| 19 | 2367468210865875600 |
| 20 | 52624238539033647864 |
| 21 | 1258531092544541563440 |