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 | 2 |
| 2 | 3 |
| 3 | 10 |
| 4 | 40 |
| 5 | 196 |
| 6 | 1176 |
| 7 | 8352 |
| 8 | 66816 |
| 9 | 589248 |
| 10 | 5892480 |
| 11 | 67841280 |
| 12 | 814095360 |
| 13 | 9007096320 |
| 14 | 126099348480 |
| 15 | 3417110323200 |
| 16 | 54673765171200 |
| 17 | -1593137026252800 |
| 18 | -28676466472550400 |
| 19 | 6142121597716070400 |
| 20 | 122842431954321408000 |
| 21 | -24453765000305786880000 |