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) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 36 |
| 5 | 220 |
| 6 | 1320 |
| 7 | 10500 |
| 8 | 84000 |
| 9 | 828576 |
| 10 | 8285760 |
| 11 | 97796160 |
| 12 | 1173553920 |
| 13 | 16145775360 |
| 14 | 226040855040 |
| 15 | 3554072121600 |
| 16 | 56865153945600 |
| 17 | 1006228442419200 |
| 18 | 18112111963545600 |
| 19 | 356294637348249600 |