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 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 40 |
| 5 | 242 |
| 6 | 1784 |
| 7 | 15374 |
| 8 | 151008 |
| 9 | 1669010 |
| 10 | 20503768 |
| 11 | 277049126 |
| 12 | 4083693200 |
| 13 | 65211041690 |
| 14 | 1121435565384 |
| 15 | 20662801363790 |
| 16 | 406100030507200 |
| 17 | 8480197575505442 |
| 18 | 187500501495191480 |
| 19 | 4376026842424336886 |
| 20 | 107506303414618515696 |
| 21 | 2773174380946415844266 |