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 | 4 |
| 2 | 9 |
| 3 | 30 |
| 4 | 132 |
| 5 | 720 |
| 6 | 4680 |
| 7 | 35280 |
| 8 | 302400 |
| 9 | 2903040 |
| 10 | 30844800 |
| 11 | 359251200 |
| 12 | 4550515200 |
| 13 | 62270208000 |
| 14 | 915372057600 |
| 15 | 14384418048000 |
| 16 | 240612083712000 |
| 17 | 4268249137152000 |
| 18 | 80029671321600000 |
| 19 | 1581386305314816000 |
| 20 | 32844177110384640000 |
| 21 | 715273190403932160000 |
| 22 | 16298010552775311360000 |