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 | 3 |
| 3 | 15 |
| 4 | 99 |
| 5 | 795 |
| 6 | 7485 |
| 7 | 80745 |
| 8 | 981225 |
| 9 | 13253625 |
| 10 | 196834995 |
| 11 | 3185662095 |
| 12 | 55770765435 |
| 13 | 1049572599075 |
| 14 | 21120725230605 |
| 15 | 452384160453225 |
| 16 | 10272547048388625 |
| 17 | 246434674107647025 |
| 18 | 6226347228582355875 |
| 19 | 165224032352989584975 |
| 20 | 4593512876411509125075 |