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 | 0 |
| 4 | 3 |
| 5 | 35 |
| 6 | 0 |
| 7 | 714 |
| 8 | 2835 |
| 9 | 35307 |
| 10 | 236880 |
| 11 | 3342350 |
| 12 | 28879158 |
| 13 | 461911086 |
| 14 | 4916519608 |
| 15 | 87798024300 |
| 16 | 1112716544355 |
| 17 | 21957112744083 |
| 18 | 322944848419392 |
| 19 | 6986165252185782 |
| 20 | 116941654550250258 |
| 21 | 2754405555107729418 |
| 22 | 51688464405692879688 |