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 | -1 |
| 2 | 3 |
| 3 | -10 |
| 4 | 40 |
| 5 | -190 |
| 6 | 1050 |
| 7 | -6620 |
| 8 | 46800 |
| 9 | -365300 |
| 10 | 3103100 |
| 11 | -28269800 |
| 12 | 271627200 |
| 13 | -2691559000 |
| 14 | 26495469000 |
| 15 | -238131478000 |
| 16 | 1394099824000 |
| 17 | 15194495654000 |
| 18 | -936096296850000 |
| 19 | 29697351895900000 |
| 20 | -819329864480400000 |
| 21 | 21683886333440500000 |
| 22 | -570263312237604700000 |
| 23 | 15145164178973569000000 |