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 | -4 |
| 4 | 3 |
| 5 | 28 |
| 6 | -15 |
| 7 | -288 |
| 8 | 105 |
| 9 | 3984 |
| 10 | -945 |
| 11 | -70080 |
| 12 | 10395 |
| 13 | 1506240 |
| 14 | -135135 |
| 15 | -38384640 |
| 16 | 2027025 |
| 17 | 1133072640 |
| 18 | -34459425 |
| 19 | -38038533120 |
| 20 | 654729075 |
| 21 | 1431213235200 |
| 22 | -13749310575 |
| 23 | -59645279232000 |
| 24 | 316234143225 |
| 25 | 2726781752217600 |
| 26 | -7905853580625 |
| 27 | -135661078090137600 |
| 28 | 213458046676875 |