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) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 10 |
| 6 | 60 |
| 7 | 462 |
| 8 | 3920 |
| 9 | 36954 |
| 10 | 382740 |
| 11 | 4327510 |
| 12 | 53088888 |
| 13 | 702756210 |
| 14 | 9988248956 |
| 15 | 151751644590 |
| 16 | 2454798429600 |
| 17 | 42130249479562 |
| 18 | 764681923900260 |
| 19 | 14636063499474054 |
| 20 | 294639009867223880 |