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 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 48 |
| 6 | 250 |
| 7 | 1760 |
| 8 | 12502 |
| 9 | 111776 |
| 10 | 1017060 |
| 11 | 11165280 |
| 12 | 123760560 |
| 13 | 1602344832 |
| 14 | 21025461600 |
| 15 | 314958758400 |
| 16 | 4765553385120 |
| 17 | 80958196300800 |
| 18 | 1386261729792960 |
| 19 | 26344715667079680 |
| 20 | 502986050203680000 |
| 21 | 10556482426015426560 |
| 22 | 222685725334400064000 |