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 | 2 |
| 3 | 9 |
| 4 | 44 |
| 5 | 450 |
| 6 | 2754 |
| 7 | 45360 |
| 8 | 340304 |
| 9 | 6481944 |
| 10 | 81801000 |
| 11 | 1370631240 |
| 12 | 21731534472 |
| 13 | 511117017840 |
| 14 | 8113055559504 |
| 15 | 193958323289640 |
| 16 | 4765385232157440 |
| 17 | 108183734293844160 |
| 18 | 2754467397591689664 |
| 19 | 80416694712647352960 |
| 20 | 2132862160676063137920 |
| 21 | 67803682111729108433280 |