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 | -2 |
| 3 | 6 |
| 4 | -21 |
| 5 | 80 |
| 6 | -320 |
| 7 | 1326 |
| 8 | -5637 |
| 9 | 24434 |
| 10 | -107541 |
| 11 | 479192 |
| 12 | -2157027 |
| 13 | 9792618 |
| 14 | -44780207 |
| 15 | 206053429 |
| 16 | -953296364 |
| 17 | 4431418833 |
| 18 | -20686477329 |
| 19 | 96930426941 |
| 20 | -455717114981 |
| 21 | 2149060994827 |
| 22 | -10162417338993 |
| 23 | 48176297258115 |
| 24 | -228910042632050 |
| 25 | 1089957826522693 |
| 26 | -5199911987465160 |