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 | -1 |
| 2 | 1 |
| 3 | 19 |
| 4 | -39 |
| 5 | 20 |
| 6 | -1513 |
| 7 | 4705 |
| 8 | -4872 |
| 9 | 1680 |
| 10 | 315523 |
| 11 | -1314807 |
| 12 | 2052644 |
| 13 | -1422960 |
| 14 | 369600 |
| 15 | -136085041 |
| 16 | 710968441 |
| 17 | -1484552160 |
| 18 | 1548707160 |
| 19 | -807206400 |
| 20 | 168168000 |
| 21 | 105261234643 |
| 22 | -661231439271 |
| 23 | 1729495989332 |
| 24 | -2410936679424 |
| 25 | 1889230062720 |
| 26 | -789044256000 |
| 27 | 137225088000 |