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 | 0 |
| 4 | -1 |
| 5 | 1 |
| 6 | -3 |
| 7 | 6 |
| 8 | -15 |
| 9 | 36 |
| 10 | -91 |
| 11 | 232 |
| 12 | -603 |
| 13 | 1585 |
| 14 | -4213 |
| 15 | 11298 |
| 16 | -30537 |
| 17 | 83097 |
| 18 | -227475 |
| 19 | 625992 |
| 20 | -1730787 |
| 21 | 4805595 |
| 22 | -13393689 |
| 23 | 37458330 |
| 24 | -105089229 |
| 25 | 295673994 |
| 26 | -834086421 |
| 27 | 2358641376 |
| 28 | -6684761125 |
| 29 | 18985057351 |
| 30 | -54022715451 |