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 | 0 |
| 1 | 0 |
| 2 | 4 |
| 3 | 44 |
| 4 | 408 |
| 5 | 3688 |
| 6 | 33212 |
| 7 | 298932 |
| 8 | 2690416 |
| 9 | 24213776 |
| 10 | 217924020 |
| 11 | 1961316220 |
| 12 | 17651846024 |
| 13 | 158866614264 |
| 14 | 1429799528428 |
| 15 | 12868195755908 |
| 16 | 115813761803232 |
| 17 | 1042323856229152 |
| 18 | 9380914706062436 |
| 19 | 84428232354561996 |
| 20 | 759854091191058040 |