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 | 1 |
| 3 | 6 |
| 4 | 80 |
| 5 | 1666 |
| 6 | 47232 |
| 7 | 1694704 |
| 8 | 73552752 |
| 9 | 3744491970 |
| 10 | 218684051648 |
| 11 | 14406896813608 |
| 12 | 1056681951098592 |
| 13 | 85379764462169382 |
| 14 | 7534286318509305600 |
| 15 | 720884741940337283712 |
| 16 | 74330131862002429961712 |
| 17 | 8215901579822006354547330 |
| 18 | 969069489665924620416715008 |