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 | 10 |
| 4 | 48 |
| 5 | 336 |
| 6 | 2400 |
| 7 | 22240 |
| 8 | 220416 |
| 9 | 2496256 |
| 10 | 30286080 |
| 11 | 411725568 |
| 12 | 6004838400 |
| 13 | 94609106944 |
| 14 | 1588301524992 |
| 15 | 28577718427648 |
| 16 | 546685777182720 |
| 17 | 11027370474504192 |
| 18 | 234498341381603328 |
| 19 | 5253826506085629952 |
| 20 | 123695389756163358720 |
| 21 | 3039894623920125116416 |