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 | 0 |
| 3 | -16 |
| 4 | 65 |
| 5 | -560 |
| 6 | 3536 |
| 7 | -25025 |
| 8 | 169456 |
| 9 | -1166880 |
| 10 | 7983745 |
| 11 | -54758496 |
| 12 | 375223200 |
| 13 | -2572072321 |
| 14 | 17628580320 |
| 15 | -120829829680 |
| 16 | 828175410881 |
| 17 | -5676410656400 |
| 18 | 38906666170736 |
| 19 | -266670338968385 |
| 20 | 1827785480332240 |
| 21 | -12527828615754816 |
| 22 | 85867013279034625 |
| 23 | -588541268397840576 |
| 24 | 4033921854875707200 |
| 25 | -27648911743562183425 |