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) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 112 |
| 5 | 662 |
| 6 | 4596 |
| 7 | 34032 |
| 8 | 268280 |
| 9 | 2201634 |
| 10 | 18679362 |
| 11 | 162611904 |
| 12 | 1446148032 |
| 13 | 13090979394 |
| 14 | 120303384120 |
| 15 | 1119971272340 |
| 16 | 10544483234056 |
| 17 | 100261309326082 |
| 18 | 961692928106614 |
| 19 | 9296529143261548 |
| 20 | 90497666895840376 |