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 | 0 |
| 1 | 1 |
| 2 | 12 |
| 3 | 252 |
| 4 | 4320 |
| 5 | 79056 |
| 6 | 1415232 |
| 7 | 25520832 |
| 8 | 459095040 |
| 9 | 8265390336 |
| 10 | 148766948352 |
| 11 | 2677865536512 |
| 12 | 48201216860160 |
| 13 | 867624080265216 |
| 14 | 15617220384079872 |
| 15 | 281110045277601792 |
| 16 | 5059980344811847680 |
| 17 | 91079649027723165696 |
| 18 | 1639433665572357537792 |
| 19 | 29509806081862392348672 |