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 | 24 |
| 3 | 182 |
| 4 | 1200 |
| 5 | 7502 |
| 6 | 45864 |
| 7 | 277622 |
| 8 | 1672800 |
| 9 | 10057502 |
| 10 | 60406104 |
| 11 | 362617862 |
| 12 | 2176246800 |
| 13 | 13059091502 |
| 14 | 78359364744 |
| 15 | 470170602902 |
| 16 | 2821066795200 |
| 17 | 16926530173502 |
| 18 | 101559568985784 |
| 19 | 609358577224742 |
| 20 | 3656154952230000 |