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 | 160 |
| 5 | 1720 |
| 6 | 13056 |
| 7 | 82656 |
| 8 | 470016 |
| 9 | 2496384 |
| 10 | 12666880 |
| 11 | 62250496 |
| 12 | 298868736 |
| 13 | 1409660928 |
| 14 | 6556483584 |
| 15 | 30148976640 |
| 16 | 137316794368 |
| 17 | 620328091648 |
| 18 | 2782435737600 |
| 19 | 12402204475392 |
| 20 | 54971691171840 |
| 21 | 242433274675200 |