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 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 18 |
| 6 | 96 |
| 7 | 600 |
| 8 | 4320 |
| 9 | 35280 |
| 10 | 322560 |
| 11 | 3265920 |
| 12 | 36288000 |
| 13 | 439084800 |
| 14 | 5748019200 |
| 15 | 80951270400 |
| 16 | 1220496076800 |
| 17 | 19615115520000 |
| 18 | 334764638208000 |
| 19 | 6046686277632000 |
| 20 | 115242726703104000 |
| 21 | 2311256907767808000 |
| 22 | 48658040163532800000 |
| 23 | 1072909785605898240000 |