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 | -13 |
| 4 | 59 |
| 5 | -269 |
| 6 | 1227 |
| 7 | -5597 |
| 8 | 25531 |
| 9 | -116461 |
| 10 | 531243 |
| 11 | -2423293 |
| 12 | 11053979 |
| 13 | -50423309 |
| 14 | 230008587 |
| 15 | -1049196317 |
| 16 | 4785964411 |
| 17 | -21831429421 |
| 18 | 99585218283 |
| 19 | -454263232573 |
| 20 | 2072145726299 |
| 21 | -9452202166349 |
| 22 | 43116719379147 |