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 | 12 |
| 4 | 72 |
| 5 | 480 |
| 6 | 3960 |
| 7 | 40320 |
| 8 | 463680 |
| 9 | 5866560 |
| 10 | 82857600 |
| 11 | 1297296000 |
| 12 | 22133865600 |
| 13 | 407869862400 |
| 14 | 8096683795200 |
| 15 | 172405968134400 |
| 16 | 3915525770956800 |
| 17 | 94443904345190400 |
| 18 | 2412049832704512000 |
| 19 | 65035187612185190400 |
| 20 | 1845812342328514560000 |