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 | 1 |
| 4 | -3 |
| 5 | -18 |
| 6 | -124 |
| 7 | -1174 |
| 8 | -12150 |
| 9 | -141536 |
| 10 | -1816780 |
| 11 | -25461723 |
| 12 | -386593670 |
| 13 | -6320496592 |
| 14 | -110711177281 |
| 15 | -2068814967831 |
| 16 | -41089562943757 |
| 17 | -864563028340432 |
| 18 | -19214971769126974 |
| 19 | -449887669808788433 |
| 20 | -11069673481210168218 |
| 21 | -285604488897863640237 |