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 | 6 |
| 3 | 78 |
| 4 | 1576 |
| 5 | 43320 |
| 6 | 1507824 |
| 7 | 63549808 |
| 8 | 3145681536 |
| 9 | 178865283456 |
| 10 | 11488065875200 |
| 11 | 822528662774016 |
| 12 | 64957295774721024 |
| 13 | 5609010346397166592 |
| 14 | 525718830294548330496 |
| 15 | 53154054477553828608000 |
| 16 | 5766597997397483718344704 |
| 17 | 668177890990349738366042112 |
| 18 | 82355042760252520538828242944 |