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 | 3 |
| 4 | 15 |
| 5 | 135 |
| 6 | 1875 |
| 7 | 38745 |
| 8 | 1168545 |
| 9 | 50017905 |
| 10 | 3029330745 |
| 11 | 257116925835 |
| 12 | 30546104308335 |
| 13 | 5065906139629335 |
| 14 | 1172940061645387035 |
| 15 | 379092680506164049425 |
| 16 | 171204492289446788997825 |
| 17 | 108139946568584292606269025 |
| 18 | 95671942593719946611454522225 |