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 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 18 |
| 5 | 72 |
| 6 | 720 |
| 7 | 4320 |
| 8 | 50400 |
| 9 | 403200 |
| 10 | 5443200 |
| 11 | 54432000 |
| 12 | 838252800 |
| 13 | 10059033600 |
| 14 | 174356582400 |
| 15 | 2440992153600 |
| 16 | 47076277248000 |
| 17 | 753220435968000 |
| 18 | 16005934264320000 |
| 19 | 288106816757760000 |
| 20 | 6690480522485760000 |
| 21 | 133809610449715200000 |
| 22 | 3372002183332823040000 |