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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | -1 |
| 5 | -5 |
| 6 | -15 |
| 7 | -35 |
| 8 | -35 |
| 9 | 504 |
| 10 | 6090 |
| 11 | 45870 |
| 12 | 270930 |
| 13 | 1215500 |
| 14 | 1995994 |
| 15 | -42118440 |
| 16 | -733409495 |
| 17 | -8069463780 |
| 18 | -70153266240 |
| 19 | -468024155016 |
| 20 | -1498366231020 |
| 21 | 21132982355940 |
| 22 | 568009017066260 |
| 23 | 8607952077741940 |
| 24 | 101448276642079059 |
| 25 | 937291639168833850 |