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 | 0 |
| 2 | 2 |
| 3 | -3 |
| 4 | 44 |
| 5 | -210 |
| 6 | 2694 |
| 7 | -23520 |
| 8 | 330672 |
| 9 | -4168584 |
| 10 | 67622040 |
| 11 | -1095648840 |
| 12 | 20621674776 |
| 13 | -403514963280 |
| 14 | 8734659594192 |
| 15 | -199049377658040 |
| 16 | 4894304369356800 |
| 17 | -126907901533425600 |
| 18 | 3501394314254828352 |
| 19 | -101643840316833194880 |
| 20 | 3112491474764866339200 |