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 | 4 |
| 2 | -4 |
| 3 | 0 |
| 4 | 136 |
| 5 | -1152 |
| 6 | 5152 |
| 7 | 0 |
| 8 | -230560 |
| 9 | 2267136 |
| 10 | -11355008 |
| 11 | 0 |
| 12 | 594412800 |
| 13 | -6184304640 |
| 14 | 32458736640 |
| 15 | 0 |
| 16 | -1828185954816 |
| 17 | 19583341166592 |
| 18 | -105435193825280 |
| 19 | 0 |
| 20 | 6195266435870720 |
| 21 | -67554137604096000 |
| 22 | 369569533686562816 |
| 23 | 0 |
| 24 | -22322916873246359552 |
| 25 | 246346071588005216256 |