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 | 5 |
| 3 | 20 |
| 4 | 90 |
| 5 | 440 |
| 6 | 2236 |
| 7 | 11720 |
| 8 | 62960 |
| 9 | 344690 |
| 10 | 1916170 |
| 11 | 10787762 |
| 12 | 61380770 |
| 13 | 352410760 |
| 14 | 2039099640 |
| 15 | 11878519460 |
| 16 | 69608606348 |
| 17 | 410056995475 |
| 18 | 2426936098575 |
| 19 | 14424334077975 |
| 20 | 86055337016695 |
| 21 | 515170271387970 |
| 22 | 3093724519080210 |
| 23 | 18631778892165080 |