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 | -8 |
| 4 | 21 |
| 5 | -49 |
| 6 | 120 |
| 7 | -288 |
| 8 | 697 |
| 9 | -1681 |
| 10 | 4060 |
| 11 | -9800 |
| 12 | 23661 |
| 13 | -57121 |
| 14 | 137904 |
| 15 | -332928 |
| 16 | 803761 |
| 17 | -1940449 |
| 18 | 4684660 |
| 19 | -11309768 |
| 20 | 27304197 |
| 21 | -65918161 |
| 22 | 159140520 |
| 23 | -384199200 |
| 24 | 927538921 |
| 25 | -2239277041 |
| 26 | 5406093004 |
| 27 | -13051463048 |
| 28 | 31509019101 |
| 29 | -76069501249 |
| 30 | 183648021600 |