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 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 1 |
| 6 | -3 |
| 7 | 18 |
| 8 | -121 |
| 9 | 1044 |
| 10 | -11112 |
| 11 | 142419 |
| 12 | -2164506 |
| 13 | 38488964 |
| 14 | -791648701 |
| 15 | 18649007091 |
| 16 | -498838420314 |
| 17 | 15036512507141 |
| 18 | -507331242588268 |
| 19 | 19044960439970134 |
| 20 | -791159753019542794 |