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 | 2 |
| 3 | 6 |
| 4 | 56 |
| 5 | 480 |
| 6 | 5664 |
| 7 | 75600 |
| 8 | 1182208 |
| 9 | 20829312 |
| 10 | 410768640 |
| 11 | 8943010560 |
| 12 | 213187497984 |
| 13 | 5520777799680 |
| 14 | 154333888579584 |
| 15 | 4631752470159360 |
| 16 | 148523272512307200 |
| 17 | 5067610703150284800 |
| 18 | 183308248516478828544 |
| 19 | 7006773595450681589760 |
| 20 | 282194468488468121518080 |