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 | -2 |
| 3 | 4 |
| 4 | -24 |
| 5 | 16 |
| 6 | -224 |
| 7 | 64 |
| 8 | -1920 |
| 9 | 256 |
| 10 | -15872 |
| 11 | 1024 |
| 12 | -129024 |
| 13 | 4096 |
| 14 | -1040384 |
| 15 | 16384 |
| 16 | -8355840 |
| 17 | 65536 |
| 18 | -66977792 |
| 19 | 262144 |
| 20 | -536346624 |
| 21 | 1048576 |
| 22 | -4292870144 |
| 23 | 4194304 |
| 24 | -34351349760 |
| 25 | 16777216 |
| 26 | -274844352512 |
| 27 | 67108864 |
| 28 | -2198889037824 |
| 29 | 268435456 |
| 30 | -17591649173504 |
| 31 | 1073741824 |