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 | 1 |
| 4 | -5 |
| 5 | -17 |
| 6 | 83 |
| 7 | 593 |
| 8 | -2893 |
| 9 | -36101 |
| 10 | 172195 |
| 11 | 3421285 |
| 12 | -15520165 |
| 13 | -467129785 |
| 14 | 1954015955 |
| 15 | 86971636825 |
| 16 | -323371713725 |
| 17 | -21196564551725 |
| 18 | 66760541581475 |
| 19 | 6552909294409325 |
| 20 | -16279195926455125 |
| 21 | -2506384727801998625 |
| 22 | 4330877561309153875 |