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 | 3 |
| 3 | 9 |
| 4 | 33 |
| 5 | 137 |
| 6 | 619 |
| 7 | 3017 |
| 8 | 15617 |
| 9 | 84625 |
| 10 | 474771 |
| 11 | 2723721 |
| 12 | 15730209 |
| 13 | 89487257 |
| 14 | 482793211 |
| 15 | 2259370697 |
| 16 | 6292321025 |
| 17 | -41172399839 |
| 18 | -1066104760797 |
| 19 | -14517156416247 |
| 20 | -163539106749663 |
| 21 | -1652237279663959 |
| 22 | -15169567281615221 |