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 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 78 |
| 5 | 332 |
| 6 | 1516 |
| 7 | 7240 |
| 8 | 35734 |
| 9 | 180620 |
| 10 | 929940 |
| 11 | 4858328 |
| 12 | 25687052 |
| 13 | 137177016 |
| 14 | 738819672 |
| 15 | 4008435984 |
| 16 | 21886788582 |
| 17 | 120178329740 |
| 18 | 663179894788 |
| 19 | 3675923244856 |
| 20 | 20456707469540 |
| 21 | 114254175491304 |
| 22 | 640223315385576 |