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 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 39 |
| 5 | 300 |
| 6 | 2715 |
| 7 | 28350 |
| 8 | 335265 |
| 9 | 4422600 |
| 10 | 64298745 |
| 11 | 1020477150 |
| 12 | 17542820295 |
| 13 | 324552648420 |
| 14 | 6426708843555 |
| 15 | 135573281994150 |
| 16 | 3034400481137025 |
| 17 | 71801374285040400 |
| 18 | 1790523094644709425 |
| 19 | 46923435009924823350 |
| 20 | 1289032229351717425575 |