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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 3 |
| 5 | -10 |
| 6 | -30 |
| 7 | 112 |
| 8 | 588 |
| 9 | -2448 |
| 10 | -18960 |
| 11 | 87296 |
| 12 | 911328 |
| 13 | -4599296 |
| 14 | -61152000 |
| 15 | 335523840 |
| 16 | 5464904448 |
| 17 | -32363874304 |
| 18 | -627708979200 |
| 19 | 3987441516544 |
| 20 | 90133968949248 |
| 21 | -610866587369472 |
| 22 | -15823700431503360 |
| 23 | 113884455221854208 |
| 24 | 3334995367266582528 |
| 25 | -25385597162671308800 |