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 | 5 |
| 3 | 26 |
| 4 | 126 |
| 5 | 408 |
| 6 | -1704 |
| 7 | -51696 |
| 8 | -555408 |
| 9 | -1217664 |
| 10 | 93550464 |
| 11 | 2424183552 |
| 12 | 30038190336 |
| 13 | -114098181120 |
| 14 | -16707096806400 |
| 15 | -459530721441792 |
| 16 | -5231858686838784 |
| 17 | 130925278326915072 |
| 18 | 9038174050387722240 |
| 19 | 246578101419998380032 |
| 20 | 1534994756662100557824 |