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 | 1 |
| 2 | 13 |
| 3 | 122 |
| 4 | 1028 |
| 5 | 8328 |
| 6 | 66576 |
| 7 | 530464 |
| 8 | 4227136 |
| 9 | 33718400 |
| 10 | 269222144 |
| 11 | 2151154176 |
| 12 | 17196647424 |
| 13 | 137514452992 |
| 14 | 1099847176192 |
| 15 | 8797569425408 |
| 16 | 70375186644992 |
| 17 | 562977870741504 |
| 18 | 4503719886520320 |
| 19 | 36029312415170560 |
| 20 | 288232575175229440 |
| 21 | 2305852355063054336 |