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 | 25 |
| 4 | 211 |
| 5 | 2238 |
| 6 | 28560 |
| 7 | 425808 |
| 8 | 7261200 |
| 9 | 139367278 |
| 10 | 2973006344 |
| 11 | 69775267186 |
| 12 | 1786673529746 |
| 13 | 49565881948204 |
| 14 | 1480900541242572 |
| 15 | 47407364553205448 |
| 16 | 1618838460981098680 |
| 17 | 58734896900587841824 |
| 18 | 2256402484187691207152 |
| 19 | 91499934912942249975504 |
| 20 | 3905739517580787866827872 |