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 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 54 |
| 5 | 460 |
| 6 | 3890 |
| 7 | 42364 |
| 8 | 512806 |
| 9 | 6698724 |
| 10 | 98496252 |
| 11 | 1585046584 |
| 12 | 27568171818 |
| 13 | 520043947020 |
| 14 | 10550553510016 |
| 15 | 228796551051436 |
| 16 | 5291441028244966 |
| 17 | 129967582592816500 |
| 18 | 3377869204044947060 |
| 19 | 92652519380506887784 |
| 20 | 2674716530794339146244 |