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 | 1 |
| 3 | 0 |
| 4 | 3 |
| 5 | 24 |
| 6 | 15 |
| 7 | 504 |
| 8 | 105 |
| 9 | 9072 |
| 10 | 436401 |
| 11 | 166320 |
| 12 | 28750491 |
| 13 | 3243240 |
| 14 | 1307809503 |
| 15 | 27965161224 |
| 16 | 52309001745 |
| 17 | 3795543015264 |
| 18 | 2000776242465 |
| 19 | 324424646818272 |
| 20 | 17268536366932851 |
| 21 | 22708075360010040 |
| 22 | 3974396337125445231 |
| 23 | 1436250980764880280 |
| 24 | 548178165969608527353 |