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 | 4 |
| 4 | 30 |
| 5 | 168 |
| 6 | 840 |
| 7 | 3960 |
| 8 | 18018 |
| 9 | 80080 |
| 10 | 350064 |
| 11 | 1511640 |
| 12 | 6466460 |
| 13 | 27457584 |
| 14 | 115892400 |
| 15 | 486748080 |
| 16 | 2035917450 |
| 17 | 8485840800 |
| 18 | 35263382880 |
| 19 | 146157442200 |
| 20 | 604404010980 |
| 21 | 2494365759600 |
| 22 | 10275832148400 |
| 23 | 42264944401680 |
| 24 | 173588164506900 |
| 25 | 712027089322848 |
| 26 | 2917167840871200 |
| 27 | 11938779496898800 |