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 | 0 |
| 3 | 1 |
| 4 | -4 |
| 5 | 26 |
| 6 | -212 |
| 7 | 2108 |
| 8 | -24720 |
| 9 | 334072 |
| 10 | -5112544 |
| 11 | 87396728 |
| 12 | -1650607040 |
| 13 | 34132685120 |
| 14 | -767025716736 |
| 15 | 18612106195456 |
| 16 | -485013257865472 |
| 17 | 13509071081429888 |
| 18 | -400505695457942528 |
| 19 | 12592502771190979712 |
| 20 | -418524228123134068224 |