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 | -1 |
| 3 | 4 |
| 4 | -3 |
| 5 | 136 |
| 6 | -1685 |
| 7 | 26496 |
| 8 | -433783 |
| 9 | 8415856 |
| 10 | -184328649 |
| 11 | 4515376240 |
| 12 | -121983339731 |
| 13 | 3605788384056 |
| 14 | -115769790754813 |
| 15 | 4012378854562456 |
| 16 | -149305859447213295 |
| 17 | 5937271828722146656 |
| 18 | -251273782851599681297 |
| 19 | 11276632158754470014304 |