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 | 2 |
| 3 | -5 |
| 4 | 14 |
| 5 | -42 |
| 6 | 132 |
| 7 | -429 |
| 8 | 1430 |
| 9 | -4862 |
| 10 | 16796 |
| 11 | -58786 |
| 12 | 208012 |
| 13 | -742900 |
| 14 | 2674440 |
| 15 | -9694845 |
| 16 | 35357670 |
| 17 | -129644790 |
| 18 | 477638700 |
| 19 | -1767263190 |
| 20 | 6564120420 |
| 21 | -24466267020 |
| 22 | 91482563640 |
| 23 | -343059613650 |
| 24 | 1289904147324 |
| 25 | -4861946401452 |
| 26 | 18367353072152 |
| 27 | -69533550916004 |