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 | 0 |
| 1 | 3 |
| 2 | -3 |
| 3 | 10 |
| 4 | -51 |
| 5 | 348 |
| 6 | -2970 |
| 7 | 30420 |
| 8 | -363510 |
| 9 | 4964400 |
| 10 | -76272840 |
| 11 | 1302058800 |
| 12 | -24450287400 |
| 13 | 500871016800 |
| 14 | -11115524019600 |
| 15 | 265655410020000 |
| 16 | -6802532278542000 |
| 17 | 185802383710944000 |
| 18 | -5392136656290384000 |
| 19 | 165689154918679392000 |
| 20 | -5374132518684161232000 |
| 21 | 183484361312817364800000 |