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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 5 |
| 4 | -35 |
| 5 | 204 |
| 6 | -1294 |
| 7 | 16862 |
| 8 | -225266 |
| 9 | 2346712 |
| 10 | -31689336 |
| 11 | 558727872 |
| 12 | -9891952608 |
| 13 | 185546362416 |
| 14 | -3668674300992 |
| 15 | 83728926109488 |
| 16 | -2078005263610704 |
| 17 | 50908186083448320 |
| 18 | -1343594571773137536 |
| 19 | 38998680958184088960 |
| 20 | -1181298578244977897856 |
| 21 | 37029733866954589964544 |