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 | -2 |
| 3 | 9 |
| 4 | -32 |
| 5 | 225 |
| 6 | -1044 |
| 7 | 11515 |
| 8 | -53696 |
| 9 | 1056321 |
| 10 | -2809700 |
| 11 | 164953371 |
| 12 | 374457744 |
| 13 | 42734920657 |
| 14 | 415505963068 |
| 15 | 17518516958475 |
| 16 | 310367497789696 |
| 17 | 10529847396874497 |
| 18 | 258747727039635132 |
| 19 | 8599295530916762779 |
| 20 | 258064489282796717200 |
| 21 | 9014901067536225062481 |