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 | -1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 26 |
| 6 | -6 |
| 7 | 414 |
| 8 | -624 |
| 9 | -288 |
| 10 | -20880 |
| 11 | 164880 |
| 12 | -9756000 |
| 13 | 43529760 |
| 14 | -324404640 |
| 15 | -4052492640 |
| 16 | -48521410560 |
| 17 | 1168445053440 |
| 18 | -26858914467840 |
| 19 | 341240066334720 |
| 20 | -5752671815116800 |
| 21 | 49267037136844800 |
| 22 | -769468911734476800 |
| 23 | 39863275492626432000 |