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 | 0 |
| 4 | 6 |
| 5 | -16 |
| 6 | 16 |
| 7 | -34 |
| 8 | 217 |
| 9 | -681 |
| 10 | 1343 |
| 11 | -3466 |
| 12 | 13370 |
| 13 | -42380 |
| 14 | 109477 |
| 15 | -312448 |
| 16 | 1040248 |
| 17 | -3267138 |
| 18 | 9447529 |
| 19 | -28367596 |
| 20 | 90504001 |
| 21 | -283611105 |
| 22 | 861087913 |
| 23 | -2654231074 |
| 24 | 8386506600 |
| 25 | -26359974392 |
| 26 | 81902319183 |
| 27 | -256179313766 |
| 28 | 809890745232 |
| 29 | -2557697524240 |
| 30 | 8046530976599 |