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 | -1 |
| 3 | 3 |
| 4 | -6 |
| 5 | 18 |
| 6 | -45 |
| 7 | 136 |
| 8 | -378 |
| 9 | 1156 |
| 10 | -3405 |
| 11 | 10549 |
| 12 | -32175 |
| 13 | 100915 |
| 14 | -314834 |
| 15 | 998323 |
| 16 | -3163683 |
| 17 | 10127020 |
| 18 | -32462265 |
| 19 | 104751043 |
| 20 | -338742887 |
| 21 | 1100559573 |
| 22 | -3583933846 |
| 23 | 11711868458 |
| 24 | -38358103030 |
| 25 | 125974533997 |
| 26 | -414566089320 |
| 27 | 1367353737806 |
| 28 | -4518185596293 |