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 | -4 |
| 2 | 13 |
| 3 | -51 |
| 4 | 244 |
| 5 | -1392 |
| 6 | 9260 |
| 7 | -70508 |
| 8 | 605320 |
| 9 | -5788008 |
| 10 | 61021872 |
| 11 | -703384272 |
| 12 | 8801449344 |
| 13 | -118828732032 |
| 14 | 1721888828928 |
| 15 | -26656798602240 |
| 16 | 439110126743040 |
| 17 | -7669109089082880 |
| 18 | 141557837068938240 |
| 19 | -2753560001544053760 |
| 20 | 56299265625742848000 |