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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 40 |
| 6 | 120 |
| 7 | 336 |
| 8 | 2128 |
| 9 | 13392 |
| 10 | 118800 |
| 11 | 850960 |
| 12 | 6004416 |
| 13 | 38408448 |
| 14 | 260321152 |
| 15 | 1744135680 |
| 16 | 17067141120 |
| 17 | 167200393216 |
| 18 | 1838196972288 |
| 19 | 18345298804992 |
| 20 | 181218866222080 |
| 21 | 1673804042803200 |
| 22 | 16992835499329536 |