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 | 0 |
| 3 | 15 |
| 4 | 110 |
| 5 | 1095 |
| 6 | 10326 |
| 7 | 107056 |
| 8 | 1149126 |
| 9 | 12845166 |
| 10 | 147817170 |
| 11 | 1743640902 |
| 12 | 20987930112 |
| 13 | 256987965373 |
| 14 | 3192889862238 |
| 15 | 40171643818920 |
| 16 | 510996955110550 |
| 17 | 6563060603543652 |
| 18 | 85017386945583408 |
| 19 | 1109744672540225361 |
| 20 | 14585261031466256370 |
| 21 | 192882251992018723947 |