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 | -47 |
| 5 | 239 |
| 6 | -239 |
| 7 | -11761 |
| 8 | 170689 |
| 9 | -1237825 |
| 10 | -2360159 |
| 11 | 238756319 |
| 12 | -4146035519 |
| 13 | 32586126143 |
| 14 | 359988680689 |
| 15 | -18567245926321 |
| 16 | 351652342984321 |
| 17 | -2283764958280321 |
| 18 | -89760640709677247 |
| 19 | 3866819337993369023 |
| 20 | -74731210747948586879 |
| 21 | 167887841949213912959 |