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 | 4 |
| 3 | 20 |
| 4 | 144 |
| 5 | 1245 |
| 6 | 12473 |
| 7 | 120213 |
| 8 | 1067757 |
| 9 | 8508432 |
| 10 | 60801152 |
| 11 | 391078610 |
| 12 | 2277606189 |
| 13 | 12079172109 |
| 14 | 58646808981 |
| 15 | 261900799332 |
| 16 | 1080219903328 |
| 17 | 4129996450120 |
| 18 | 14683917874810 |
| 19 | 48687786994190 |
| 20 | 150930310833366 |