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 | -2 |
| 1 | 1 |
| 2 | -4 |
| 3 | 9 |
| 4 | -34 |
| 5 | 121 |
| 6 | -452 |
| 7 | 1681 |
| 8 | -6274 |
| 9 | 23409 |
| 10 | -87364 |
| 11 | 326041 |
| 12 | -1216802 |
| 13 | 4541161 |
| 14 | -16947844 |
| 15 | 63250209 |
| 16 | -236052994 |
| 17 | 880961761 |
| 18 | -3287794052 |
| 19 | 12270214441 |
| 20 | -45793063714 |
| 21 | 170902040409 |
| 22 | -637815097924 |
| 23 | 2380358351281 |
| 24 | -8883618307202 |
| 25 | 33154114877521 |
| 26 | -123732841202884 |