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 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 84 |
| 6 | 561 |
| 7 | 4260 |
| 8 | 36413 |
| 9 | 346276 |
| 10 | 3628801 |
| 11 | 41569064 |
| 12 | 516929544 |
| 13 | 6936548425 |
| 14 | 99917483647 |
| 15 | 1537944393896 |
| 16 | 25193549397053 |
| 17 | 437655212248536 |
| 18 | 8036723680196724 |
| 19 | 155554110186062367 |
| 20 | 3165278489148945082 |
| 21 | 67553429525569109411 |
| 22 | 1508884070229326953381 |