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 | -3 |
| 2 | 15 |
| 3 | -51 |
| 4 | 231 |
| 5 | -843 |
| 6 | 3615 |
| 7 | -13731 |
| 8 | 57111 |
| 9 | -221883 |
| 10 | 907215 |
| 11 | -3569811 |
| 12 | 14456391 |
| 13 | -57294123 |
| 14 | 230770815 |
| 15 | -918300291 |
| 16 | 3687550071 |
| 17 | -14707153563 |
| 18 | 58957754415 |
| 19 | -235443597171 |
| 20 | 942936650151 |
| 21 | -3768259816203 |
| 22 | 15083499618015 |