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 | 1 |
| 3 | 5 |
| 4 | 44 |
| 5 | 244 |
| 6 | 2064 |
| 7 | 15168 |
| 8 | 181824 |
| 9 | 1878336 |
| 10 | 21323520 |
| 11 | 238187520 |
| 12 | 3496919040 |
| 13 | 45938949120 |
| 14 | 699188474880 |
| 15 | 11185253452800 |
| 16 | 220809635020800 |
| 17 | 3774686585241600 |
| 18 | 75413794524364800 |
| 19 | 1439264469668659200 |
| 20 | 31704771803185152000 |
| 21 | 690129227948654592000 |