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) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 1 |
| 4 | 24 |
| 5 | 64 |
| 6 | 540 |
| 7 | 8640 |
| 8 | 34560 |
| 9 | 103680 |
| 10 | 3326400 |
| 11 | 23224320 |
| 12 | 96768000 |
| 13 | 764225280 |
| 14 | 24385536000 |
| 15 | 108391219200 |
| 16 | 1097349120000 |
| 17 | 29847896064000 |
| 18 | 347640201216000 |
| 19 | 12239832084480000 |
| 20 | 2008587829248000 |
| 21 | 365022211276800000 |