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 | 1 |
| 4 | 13 |
| 5 | -199 |
| 6 | 2251 |
| 7 | -19991 |
| 8 | 7001 |
| 9 | 7530193 |
| 10 | -330734249 |
| 11 | 11005284401 |
| 12 | -300961551131 |
| 13 | 4886902605001 |
| 14 | 184195977487523 |
| 15 | -28517140157423399 |
| 16 | 2322376314679777201 |
| 17 | -153646291657993064671 |
| 18 | 8388000381774954552751 |
| 19 | -287686436757241322569247 |