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 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 18 |
| 7 | 54 |
| 8 | 216 |
| 9 | 1080 |
| 10 | 5400 |
| 11 | 27000 |
| 12 | 162000 |
| 13 | 1134000 |
| 14 | 7938000 |
| 15 | 55566000 |
| 16 | 444528000 |
| 17 | 4000752000 |
| 18 | 36006768000 |
| 19 | 324060912000 |
| 20 | 3240609120000 |
| 21 | 35646700320000 |
| 22 | 392113703520000 |
| 23 | 4313250738720000 |