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 | 6 |
| 2 | 57 |
| 3 | 468 |
| 4 | 3564 |
| 5 | 25920 |
| 6 | 182736 |
| 7 | 1259712 |
| 8 | 8538048 |
| 9 | 57106944 |
| 10 | 377913600 |
| 11 | 2479113216 |
| 12 | 16144468992 |
| 13 | 104485552128 |
| 14 | 672625741824 |
| 15 | 4310029025280 |
| 16 | 27505821597696 |
| 17 | 174908814262272 |
| 18 | 1108696193630208 |
| 19 | 7007637010120704 |
| 20 | 44178581150760960 |
| 21 | 277868041444786176 |