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 | 2 |
| 3 | 18 |
| 4 | 180 |
| 5 | 2100 |
| 6 | 28350 |
| 7 | 436590 |
| 8 | 7567560 |
| 9 | 145945800 |
| 10 | 3101348250 |
| 11 | 72020198250 |
| 12 | 1814908995900 |
| 13 | 49332526343100 |
| 14 | 1438865351673750 |
| 15 | 44826189802143750 |
| 16 | 1485668004871050000 |
| 17 | 52196469237802890000 |
| 18 | 1937793920453432291250 |
| 19 | 75801938653031321981250 |
| 20 | 3116301922402398792562500 |