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 | 50 |
| 3 | 500 |
| 4 | 4375 |
| 5 | 27500 |
| 6 | 0 |
| 7 | -3562500 |
| 8 | -70078125 |
| 9 | -876562500 |
| 10 | -6926562500 |
| 11 | 0 |
| 12 | 1189169921875 |
| 13 | 25690820312500 |
| 14 | 346441406250000 |
| 15 | 2911880859375000 |
| 16 | 0 |
| 17 | -550017993164062500 |
| 18 | -12339622131347656250 |
| 19 | -171953389892578125000 |
| 20 | -1487552714691162109375 |
| 21 | 0 |