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 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 200 |
| 6 | 1230 |
| 7 | 8652 |
| 8 | 69272 |
| 9 | 623520 |
| 10 | 6235290 |
| 11 | 68588300 |
| 12 | 823059732 |
| 13 | 10699776672 |
| 14 | 149796873590 |
| 15 | 2246953104060 |
| 16 | 35951249665200 |
| 17 | 611171244308672 |
| 18 | 11001082397556402 |
| 19 | 209020565553571980 |
| 20 | 4180411311071439980 |
| 21 | 87788637532500240000 |