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 | 5 |
| 2 | -20 |
| 3 | 100 |
| 4 | 0 |
| 5 | -9625 |
| 6 | 169875 |
| 7 | -1933125 |
| 8 | 14025625 |
| 9 | 0 |
| 10 | -2065744375 |
| 11 | 41575056250 |
| 12 | -523670743750 |
| 13 | 4119815531250 |
| 14 | 0 |
| 15 | -684944792812500 |
| 16 | 14442398472421875 |
| 17 | -189324209836328125 |
| 18 | 1541918426557031250 |
| 19 | 0 |
| 20 | -271410262779871875000 |
| 21 | 5860693797318871093750 |