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 | -1 |
| 3 | 0 |
| 4 | -1 |
| 5 | 2 |
| 6 | 0 |
| 7 | -1 |
| 8 | 2 |
| 9 | -6 |
| 10 | 0 |
| 11 | -1 |
| 12 | 4 |
| 13 | -6 |
| 14 | 24 |
| 15 | 0 |
| 16 | -1 |
| 17 | 4 |
| 18 | -12 |
| 19 | 24 |
| 20 | -120 |
| 21 | 0 |
| 22 | -1 |
| 23 | 6 |
| 24 | -18 |
| 25 | 48 |
| 26 | -120 |
| 27 | 720 |
| 28 | 0 |
| 29 | -1 |
| 30 | 6 |
| 31 | -24 |
| 32 | 72 |
| 33 | -240 |
| 34 | 720 |
| 35 | -5040 |
| 36 | 0 |
| 37 | -1 |
| 38 | 8 |
| 39 | -30 |
| 40 | 120 |
| 41 | -360 |
| 42 | 1440 |
| 43 | -5040 |
| 44 | 40320 |
| 45 | 0 |
| 46 | -1 |
| 47 | 8 |
| 48 | -42 |
| 49 | 144 |
| 50 | -600 |
| 51 | 2160 |
| 52 | -10080 |
| 53 | 40320 |
| 54 | -362880 |