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 | 6 |
| 4 | -20 |
| 5 | 80 |
| 6 | -366 |
| 7 | 1904 |
| 8 | -11080 |
| 9 | 71424 |
| 10 | -505210 |
| 11 | 3891712 |
| 12 | -32433180 |
| 13 | 290787328 |
| 14 | -2791053734 |
| 15 | 28556359680 |
| 16 | -310264194320 |
| 17 | 3567710830592 |
| 18 | -43287834157938 |
| 19 | 552688817143808 |
| 20 | -7407423764750500 |
| 21 | 103981459115606016 |
| 22 | -1525675236649033822 |
| 23 | 23354749389657604096 |