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 | -3 |
| 5 | -3 |
| 6 | 1 |
| 7 | -25 |
| 8 | 49 |
| 9 | 1 |
| 10 | 385 |
| 11 | 1489 |
| 12 | 503 |
| 13 | 10753 |
| 14 | -82371 |
| 15 | -196419 |
| 16 | -1575551 |
| 17 | -12482641 |
| 18 | 95770849 |
| 19 | -739310591 |
| 20 | 5684060161 |
| 21 | 45018762529 |
| 22 | 359479836623 |
| 23 | 7751171129473 |
| 24 | -59488778593731 |
| 25 | -137028961472835 |
| 26 | -29749898850946559 |
| 27 | -441962130410844841 |