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 | 4 |
| 3 | 15 |
| 4 | 68 |
| 5 | 370 |
| 6 | 2364 |
| 7 | 17388 |
| 8 | 144864 |
| 9 | 1349136 |
| 10 | 13894560 |
| 11 | 156831840 |
| 12 | 1925527680 |
| 13 | 25550778240 |
| 14 | 364416917760 |
| 15 | 5559659078400 |
| 16 | 90349397913600 |
| 17 | 1558170228787200 |
| 18 | 28423674336153600 |
| 19 | 546807873520742400 |
| 20 | 11064204944529408000 |
| 21 | 234902850943703040000 |
| 22 | 5221386564941352960000 |