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 | -1 |
| 4 | 1 |
| 5 | 19 |
| 6 | 151 |
| 7 | 1091 |
| 8 | 7841 |
| 9 | 56519 |
| 10 | 396271 |
| 11 | 2442439 |
| 12 | 7701409 |
| 13 | -145269541 |
| 14 | -4833158329 |
| 15 | -104056218421 |
| 16 | -2002667085119 |
| 17 | -37109187217649 |
| 18 | -679877731030049 |
| 19 | -12440309297451121 |
| 20 | -227773259993414719 |
| 21 | -4155839606711748061 |
| 22 | -74724654677947488521 |