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 | 0 |
| 3 | 0 |
| 4 | 12 |
| 5 | 660 |
| 6 | 20400 |
| 7 | 445620 |
| 8 | 7977732 |
| 9 | 126860580 |
| 10 | 1873839000 |
| 11 | 26381789940 |
| 12 | 359484471852 |
| 13 | 4784481401700 |
| 14 | 62538498859200 |
| 15 | 805447464281460 |
| 16 | 10241415118476372 |
| 17 | 128722997969290020 |
| 18 | 1600670708273985000 |
| 19 | 19705915838479512180 |
| 20 | 240330009637668935292 |