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 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 72 |
| 5 | 600 |
| 6 | 5760 |
| 7 | 65520 |
| 8 | 846720 |
| 9 | 12337920 |
| 10 | 199584000 |
| 11 | 3552595200 |
| 12 | 68976230400 |
| 13 | 1450895846400 |
| 14 | 32866215782400 |
| 15 | 797681364480000 |
| 16 | 20650793619456000 |
| 17 | 568032822669312000 |
| 18 | 16543733655601152000 |
| 19 | 508598164809326592000 |
| 20 | 16458582085314969600000 |