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 | 3 |
| 3 | -8 |
| 4 | 20 |
| 5 | -51 |
| 6 | 132 |
| 7 | -339 |
| 8 | 868 |
| 9 | -2228 |
| 10 | 5720 |
| 11 | -14676 |
| 12 | 37659 |
| 13 | -96644 |
| 14 | 248004 |
| 15 | -636413 |
| 16 | 1633144 |
| 17 | -4190920 |
| 18 | 10754580 |
| 19 | -27598012 |
| 20 | 70821032 |
| 21 | -181738372 |
| 22 | 466370429 |
| 23 | -1196782952 |
| 24 | 3071141180 |
| 25 | -7881051500 |
| 26 | 20224069573 |
| 27 | -51898276576 |
| 28 | 133179482008 |
| 29 | -341760374284 |
| 30 | 877013123076 |
| 31 | -2250559385788 |