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 | 4 |
| 3 | 24 |
| 4 | 152 |
| 5 | 1010 |
| 6 | 6912 |
| 7 | 48328 |
| 8 | 343408 |
| 9 | 2471274 |
| 10 | 17966360 |
| 11 | 131717960 |
| 12 | 972488640 |
| 13 | 7223061040 |
| 14 | 53925450880 |
| 15 | 404400203280 |
| 16 | 3044645475296 |
| 17 | 23002424245754 |
| 18 | 174324246314184 |
| 19 | 1324800580881952 |
| 20 | 10093304926771600 |
| 21 | 77073430602848316 |
| 22 | 589761299099196224 |