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 | 0 |
| 1 | 2 |
| 2 | 6 |
| 3 | 32 |
| 4 | 222 |
| 5 | 1824 |
| 6 | 17016 |
| 7 | 176112 |
| 8 | 1993392 |
| 9 | 24438960 |
| 10 | 322294896 |
| 11 | 4548010032 |
| 12 | 68385367152 |
| 13 | 1091838106800 |
| 14 | 18454096189296 |
| 15 | 329306074785072 |
| 16 | 6189015238217712 |
| 17 | 122232512688657840 |
| 18 | 2531600753529542256 |