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 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 39 |
| 5 | 228 |
| 6 | 2400 |
| 7 | 23616 |
| 8 | 307692 |
| 9 | 4197408 |
| 10 | 67658769 |
| 11 | 1174316570 |
| 12 | 22916090131 |
| 13 | 482946085932 |