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 | -1 |
| 2 | -3 |
| 3 | -1 |
| 4 | 25 |
| 5 | 624 |
| 6 | 9871 |
| 7 | 170470 |
| 8 | 3027249 |
| 9 | 55077245 |
| 10 | 979330606 |
| 11 | 15079702923 |
| 12 | 94670678245 |
| 13 | -7958168036625 |
| 14 | -626145997536240 |
| 15 | -34564907982551791 |
| 16 | -1733699815491494303 |
| 17 | -84294315853736719077 |
| 18 | -4067859614343931897505 |
| 19 | -196552300464314521511610 |
| 20 | -9519733465269825759734169 |