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) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | 7 |
| 5 | 25 |
| 6 | 127 |
| 7 | 777 |
| 8 | 5547 |
| 9 | 45216 |
| 10 | 414144 |
| 11 | 4209480 |
| 12 | 47009880 |
| 13 | 572101920 |
| 14 | 7535302560 |
| 15 | 106791531840 |
| 16 | 1620314539200 |
| 17 | 26205248563200 |
| 18 | 450022496716800 |
| 19 | 8178211565798400 |
| 20 | 156798308067609600 |
| 21 | 3162998405887488000 |
| 22 | 66967168288624128000 |
| 23 | 1484773164338365440000 |