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 | -5 |
| 5 | 29 |
| 6 | -89 |
| 7 | 209 |
| 8 | 841 |
| 9 | -50905 |
| 10 | 458641 |
| 11 | -2423521 |
| 12 | 8243731 |
| 13 | 158742869 |
| 14 | -2450634185 |
| 15 | 18519809489 |
| 16 | -1402926535919 |
| 17 | 21355930009679 |
| 18 | -139305034406879 |
| 19 | 306503668195775 |
| 20 | 40578438892908331 |
| 21 | -816475138658703091 |
| 22 | 6941097158619626311 |
| 23 | -24787202385366731311 |