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 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 15 |
| 6 | 180 |
| 7 | 2100 |
| 8 | 25235 |
| 9 | 319410 |
| 10 | 4299750 |
| 11 | 61815600 |
| 12 | 950524575 |
| 13 | 15633092475 |
| 14 | 274749725250 |
| 15 | 5151569172750 |
| 16 | 102831791687625 |
| 17 | 2179782464359500 |
| 18 | 48933251188321500 |
| 19 | 1160002995644493000 |
| 20 | 28956069155772383625 |
| 21 | 759014081927743516875 |