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 | 6 |
| 2 | 54 |
| 3 | 324 |
| 4 | 1620 |
| 5 | 7290 |
| 6 | 30618 |
| 7 | 122472 |
| 8 | 472392 |
| 9 | 1771470 |
| 10 | 6495390 |
| 11 | 23383404 |
| 12 | 82904796 |
| 13 | 290166786 |
| 14 | 1004423490 |
| 15 | 3443737680 |
| 16 | 11708708112 |
| 17 | 39516889878 |
| 18 | 132497807238 |
| 19 | 441659357460 |
| 20 | 1464449448420 |
| 21 | 4832683179786 |
| 22 | 15878816162154 |