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 | 0 |
| 3 | 2 |
| 4 | 64 |
| 5 | 1090 |
| 6 | 14000 |
| 7 | 153762 |
| 8 | 1533504 |
| 9 | 14356610 |
| 10 | 128722000 |
| 11 | 1119607522 |
| 12 | 9528462944 |
| 13 | 79817940930 |
| 14 | 660876543600 |
| 15 | 5424917141282 |
| 16 | 44246078560384 |
| 17 | 359144709794050 |
| 18 | 2904688464582800 |
| 19 | 23429048035827042 |
| 20 | 188593339362097824 |