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 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 3 |
| 5 | 16 |
| 6 | 96 |
| 7 | 675 |
| 8 | 5413 |
| 9 | 48800 |
| 10 | 488592 |
| 11 | 5379333 |
| 12 | 64595975 |
| 13 | 840192288 |
| 14 | 11767626752 |
| 15 | 176574062535 |
| 16 | 2825965531593 |
| 17 | 48052401132800 |
| 18 | 865108807357216 |
| 19 | 16439727718351881 |
| 20 | 328839946389605643 |
| 21 | 6906458590966507696 |