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 | 1 |
| 4 | 15 |
| 5 | 222 |
| 6 | 3660 |
| 7 | 68295 |
| 8 | 1436568 |
| 9 | 33779340 |
| 10 | 880107840 |
| 11 | 25201854045 |
| 12 | 787368574080 |
| 13 | 26667815195274 |
| 14 | 973672928417280 |
| 15 | 38132879409281475 |
| 16 | 1594927540549217280 |
| 17 | 70964911709203684440 |
| 18 | 3347306760024413356032 |
| 19 | 166855112441313024389625 |
| 20 | 8765006377126199463936000 |