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) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 2 |
| 4 | -6 |
| 5 | -10 |
| 6 | 142 |
| 7 | -434 |
| 8 | -4478 |
| 9 | 88122 |
| 10 | -688518 |
| 11 | -4032346 |
| 12 | 268040678 |
| 13 | -5689167298 |
| 14 | 53999999466 |
| 15 | 1413830543394 |
| 16 | -98561802143670 |
| 17 | 3282601333608550 |
| 18 | -59117973090349066 |
| 19 | -1121454296035526786 |
| 20 | 171971593399059103618 |
| 21 | -10034063428244586340158 |