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 | 0 |
| 2 | 1 |
| 3 | -1 |
| 4 | 25 |
| 5 | -101 |
| 6 | 2281 |
| 7 | -19895 |
| 8 | 472305 |
| 9 | -6760297 |
| 10 | 177126121 |
| 11 | -3578690435 |
| 12 | 105341330953 |
| 13 | -2743981145933 |
| 14 | 91092111623241 |
| 15 | -2888769295882111 |
| 16 | 107832291781283809 |
| 17 | -4009180998104138321 |
| 18 | 167254334458983887689 |
| 19 | -7105017992715364001147 |
| 20 | 328862774630320838523321 |