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 | -3 |
| 4 | 9 |
| 5 | 17 |
| 6 | -145 |
| 7 | 21 |
| 8 | 2961 |
| 9 | -9119 |
| 10 | -58273 |
| 11 | 530541 |
| 12 | 177177 |
| 13 | -24815503 |
| 14 | 109736783 |
| 15 | 845196933 |
| 16 | -11562650847 |
| 17 | 9274089409 |
| 18 | 818943535295 |
| 19 | -6145817165859 |
| 20 | -30817061557719 |
| 21 | 818240768280017 |
| 22 | -3016149953173201 |
| 23 | -67401109608160779 |