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 | -2 |
| 4 | 0 |
| 5 | 10 |
| 6 | 10 |
| 7 | -60 |
| 8 | -220 |
| 9 | 400 |
| 10 | 4200 |
| 11 | 2200 |
| 12 | -90200 |
| 13 | -290400 |
| 14 | 1892000 |
| 15 | 15796000 |
| 16 | -24024000 |
| 17 | -775676000 |
| 18 | -1592492000 |
| 19 | 36509880000 |
| 20 | 240055640000 |
| 21 | -1435950560000 |
| 22 | -23703057840000 |
| 23 | 7376731120000 |
| 24 | 2082346354000000 |
| 25 | 9478853472000000 |
| 26 | -162472029808000000 |