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 | 0 |
| 2 | 4 |
| 3 | 8 |
| 4 | 72 |
| 5 | 416 |
| 6 | 3520 |
| 7 | 31104 |
| 8 | 316288 |
| 9 | 3525632 |
| 10 | 43117056 |
| 11 | 572195840 |
| 12 | 8191304704 |
| 13 | 125761056768 |
| 14 | 2060841582592 |
| 15 | 35894401335296 |
| 16 | 662066514984960 |
| 17 | 12890305925218304 |
| 18 | 264155723747688448 |
| 19 | 5682905054074109952 |
| 20 | 128051031032232411136 |
| 21 | 3015653024970577018880 |