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 | 2 |
| 2 | -4 |
| 3 | -10 |
| 4 | 30 |
| 5 | 72 |
| 6 | -238 |
| 7 | -580 |
| 8 | 1970 |
| 9 | 4910 |
| 10 | -16734 |
| 11 | -42750 |
| 12 | 144600 |
| 13 | 379000 |
| 14 | -1264700 |
| 15 | -3402480 |
| 16 | 11160730 |
| 17 | 30828070 |
| 18 | -99168820 |
| 19 | -281279030 |
| 20 | 885931600 |
| 21 | 2580541580 |
| 22 | -7948885910 |
| 23 | -23779051760 |
| 24 | 71572652480 |
| 25 | 219906488302 |
| 26 | -646332447086 |
| 27 | -2039738985238 |
| 28 | 5850898295170 |