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 | 0 |
| 2 | 4 |
| 3 | 6 |
| 4 | 56 |
| 5 | 250 |
| 6 | 1812 |
| 7 | 12614 |
| 8 | 101040 |
| 9 | 864882 |
| 10 | 7988780 |
| 11 | 78726142 |
| 12 | 823897032 |
| 13 | 9111774698 |
| 14 | 106068603396 |
| 15 | 1295153135670 |
| 16 | 16538681229152 |
| 17 | 220281968528098 |
| 18 | 3053087839536732 |
| 19 | 43941561067048430 |
| 20 | 655501502129291640 |
| 21 | 10118103843683127642 |