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 | -3 |
| 4 | -3 |
| 5 | 20 |
| 6 | 150 |
| 7 | 504 |
| 8 | -343 |
| 9 | -18180 |
| 10 | -140220 |
| 11 | -500500 |
| 12 | 2032899 |
| 13 | 50210082 |
| 14 | 441768236 |
| 15 | 1740141480 |
| 16 | -13025325615 |
| 17 | -330558552376 |
| 18 | -3452606080848 |
| 19 | -16648495695792 |
| 20 | 136964192085395 |
| 21 | 4315989335784630 |
| 22 | 55121200672923924 |
| 23 | 352945156766431592 |