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 | -12 |
| 4 | 16 |
| 5 | 400 |
| 6 | 2208 |
| 7 | -448 |
| 8 | -131840 |
| 9 | -1357056 |
| 10 | -4820480 |
| 11 | 71120896 |
| 12 | 1537308672 |
| 13 | 14006460416 |
| 14 | 3075702784 |
| 15 | -2224350781440 |
| 16 | -41354996154368 |
| 17 | -359660395495424 |
| 18 | 1675436608585728 |
| 19 | 121894823709900800 |
| 20 | 2317859245604208640 |
| 21 | 20543311167964053504 |