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 | -4 |
| 4 | 13 |
| 5 | -36 |
| 6 | 100 |
| 7 | -281 |
| 8 | 797 |
| 9 | -2281 |
| 10 | 6546 |
| 11 | -18778 |
| 12 | 53872 |
| 13 | -154662 |
| 14 | 444263 |
| 15 | -1276284 |
| 16 | 3665773 |
| 17 | -10524939 |
| 18 | 30203731 |
| 19 | -86624174 |
| 20 | 248257298 |
| 21 | -710882708 |
| 22 | 2033663952 |
| 23 | -5811660425 |
| 24 | 16588828304 |
| 25 | -47291077636 |
| 26 | 134630218334 |
| 27 | -382697080366 |
| 28 | 1086083438999 |