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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | -1 |
| 4 | 10 |
| 5 | -16 |
| 6 | 126 |
| 7 | -526 |
| 8 | 10312 |
| 9 | -30024 |
| 10 | 453840 |
| 11 | -2805408 |
| 12 | 45779328 |
| 13 | -374664720 |
| 14 | 7932770496 |
| 15 | -67692115440 |
| 16 | 2432120198016 |
| 17 | -16610113920768 |
| 18 | 437275706750208 |
| 19 | -5110200130727808 |
| 20 | 159305381515284480 |
| 21 | -1931470594025607936 |
| 22 | 63854116254680514048 |