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 | 13 |
| 4 | 83 |
| 5 | 582 |
| 6 | 4554 |
| 7 | 39672 |
| 8 | 382248 |
| 9 | 4044240 |
| 10 | 46663920 |
| 11 | 583554240 |
| 12 | 7865622720 |
| 13 | 113711230080 |
| 14 | 1755484617600 |
| 15 | 28828769356800 |
| 16 | 501858148377600 |
| 17 | 9232213174732800 |
| 18 | 178968924600883200 |
| 19 | 3646603415927808000 |
| 20 | 77916767838981120000 |
| 21 | 1742147265551616000000 |