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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 20 |
| 6 | 360 |
| 7 | 6860 |
| 8 | 143360 |
| 9 | 3306744 |
| 10 | 84000000 |
| 11 | 2338460520 |
| 12 | 70946979840 |
| 13 | 2332989862060 |
| 14 | 82726831323136 |
| 15 | 3148511132812500 |
| 16 | 128071114403348480 |
| 17 | 5546563698427324720 |
| 18 | 254873089955815096320 |
| 19 | 12387799656377835411984 |
| 20 | 635043840000000000000000 |