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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | -1 |
| 4 | 2 |
| 5 | 2 |
| 6 | -5 |
| 7 | -5 |
| 8 | 14 |
| 9 | 14 |
| 10 | -42 |
| 11 | -42 |
| 12 | 132 |
| 13 | 132 |
| 14 | -429 |
| 15 | -429 |
| 16 | 1430 |
| 17 | 1430 |
| 18 | -4862 |
| 19 | -4862 |
| 20 | 16796 |
| 21 | 16796 |
| 22 | -58786 |
| 23 | -58786 |
| 24 | 208012 |
| 25 | 208012 |
| 26 | -742900 |
| 27 | -742900 |
| 28 | 2674440 |
| 29 | 2674440 |
| 30 | -9694845 |
| 31 | -9694845 |
| 32 | 35357670 |
| 33 | 35357670 |
| 34 | -129644790 |
| 35 | -129644790 |
| 36 | 477638700 |
| 37 | 477638700 |
| 38 | -1767263190 |
| 39 | -1767263190 |