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 | 6 |
| 2 | 24 |
| 3 | 156 |
| 4 | 564 |
| 5 | 4116 |
| 6 | 12804 |
| 7 | 110676 |
| 8 | 273444 |
| 9 | 3046836 |
| 10 | 5156484 |
| 11 | 86248596 |
| 12 | 68445924 |
| 13 | 2519011956 |
| 14 | -465634236 |
| 15 | 76035992916 |
| 16 | -90005019996 |
| 17 | 2371084807476 |
| 18 | -5071235407356 |
| 19 | 76203779631636 |
| 20 | -228340841852316 |
| 21 | 2514454230801396 |