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 | 4 |
| 3 | -9 |
| 4 | 42 |
| 5 | -130 |
| 6 | 660 |
| 7 | -2415 |
| 8 | 12810 |
| 9 | -51786 |
| 10 | 281736 |
| 11 | -1216446 |
| 12 | 6727644 |
| 13 | -30440124 |
| 14 | 170316432 |
| 15 | -798126615 |
| 16 | 4504487130 |
| 17 | -21692469370 |
| 18 | 123255492360 |
| 19 | -606672653730 |
| 20 | 3465702008340 |
| 21 | -17366224451940 |
| 22 | 99645553785960 |
| 23 | -506814533253210 |
| 24 | 2918768920720380 |
| 25 | -15034038412333500 |