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 | 25 |
| 3 | 0 |
| 4 | -1250 |
| 5 | -6875 |
| 6 | 65625 |
| 7 | 1062500 |
| 8 | 0 |
| 9 | -116796875 |
| 10 | -782031250 |
| 11 | 8609375000 |
| 12 | 155390625000 |
| 13 | 0 |
| 14 | -19950927734375 |
| 15 | -141498046875000 |
| 16 | 1635108642578125 |
| 17 | 30759411621093750 |
| 18 | 0 |
| 19 | -4223049316406250000 |
| 20 | -30787073669433593750 |
| 21 | 364567847442626953125 |