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 | 2 |
| 3 | 3 |
| 4 | 40 |
| 5 | 205 |
| 6 | 2556 |
| 7 | 24409 |
| 8 | 347712 |
| 9 | 4794633 |
| 10 | 81163900 |
| 11 | 1434596581 |
| 12 | 28725779952 |
| 13 | 612610306477 |
| 14 | 14280306222924 |
| 15 | 354958921699425 |
| 16 | 9471543095892736 |
| 17 | 268347925179992593 |
| 18 | 8075532017006497404 |
| 19 | 256672899448317943453 |
| 20 | 8603440900030816095600 |