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 | -1 |
| 3 | 5 |
| 4 | 1 |
| 5 | 79 |
| 6 | -689 |
| 7 | 2981 |
| 8 | -7615 |
| 9 | -172801 |
| 10 | 3621151 |
| 11 | -16469531 |
| 12 | -240199871 |
| 13 | 2722511375 |
| 14 | 51840080111 |
| 15 | -1987808959291 |
| 16 | 12337235928961 |
| 17 | 136594696115071 |
| 18 | -1167414675803585 |
| 19 | -56631124939839931 |
| 20 | -1376838916423621759 |
| 21 | 69766591820556094799 |