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 | -2 |
| 3 | 8 |
| 4 | -20 |
| 5 | 68 |
| 6 | -188 |
| 7 | 596 |
| 8 | -1724 |
| 9 | 5300 |
| 10 | -15644 |
| 11 | 47444 |
| 12 | -141308 |
| 13 | 425972 |
| 14 | -1273820 |
| 15 | 3829652 |
| 16 | -11472572 |
| 17 | 34450484 |
| 18 | -103285916 |
| 19 | 309988820 |
| 20 | -929704316 |
| 21 | 2789637236 |
| 22 | -8367863132 |
| 23 | 25105686548 |
| 24 | -75312865340 |
| 25 | 225946984628 |
| 26 | -677824176668 |
| 27 | 2033506084436 |