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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 20 |
| 6 | 240 |
| 7 | 1470 |
| 8 | 10640 |
| 9 | 83160 |
| 10 | 584640 |
| 11 | 4496030 |
| 12 | 42658440 |
| 13 | 371762820 |
| 14 | 3594871280 |
| 15 | 38650622010 |
| 16 | 396457108320 |
| 17 | 4330689250160 |
| 18 | 53963701424640 |
| 19 | 641211774798510 |
| 20 | 8205894865096280 |
| 21 | 113786291585124060 |