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 | -5 |
| 4 | -23 |
| 5 | 121 |
| 6 | 1321 |
| 7 | -7349 |
| 8 | -148175 |
| 9 | 853777 |
| 10 | 27840241 |
| 11 | -163354949 |
| 12 | -7934320679 |
| 13 | 46820981065 |
| 14 | 3203091569497 |
| 15 | -18833438286389 |
| 16 | -1742847946697759 |
| 17 | 10137524365568161 |
| 18 | 1230956201929018465 |
| 19 | -7042544858204663813 |
| 20 | -1095864481054115534519 |