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 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 60 |
| 5 | 460 |
| 6 | 3900 |
| 7 | 39438 |
| 8 | 456288 |
| 9 | 5896224 |
| 10 | 85230000 |
| 11 | 1349017560 |
| 12 | 23353941600 |
| 13 | 437432418696 |
| 14 | 8828284404576 |
| 15 | 190867622500800 |
| 16 | 4401749312069760 |
| 17 | 107859517575659520 |
| 18 | 2798352667710645120 |
| 19 | 76636669899079699776 |
| 20 | 2209235394261812751360 |