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 | -21 |
| 4 | 220 |
| 5 | -2705 |
| 6 | 40926 |
| 7 | -733537 |
| 8 | 15124216 |
| 9 | -352606050 |
| 10 | 9174382490 |
| 11 | -263533561852 |
| 12 | 8283376452948 |
| 13 | -282795708021411 |
| 14 | 10420847619031710 |
| 15 | -412243715452039440 |
| 16 | 17425722339237083120 |
| 17 | -783844576340696848341 |
| 18 | 37384875796116662077194 |