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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | -3 |
| 4 | 6 |
| 5 | 30 |
| 6 | -120 |
| 7 | -840 |
| 8 | 5040 |
| 9 | 45360 |
| 10 | -362880 |
| 11 | -3991680 |
| 12 | 39916800 |
| 13 | 518918400 |
| 14 | -6227020800 |
| 15 | -93405312000 |
| 16 | 1307674368000 |
| 17 | 22230464256000 |
| 18 | -355687428096000 |
| 19 | -6758061133824000 |
| 20 | 121645100408832000 |
| 21 | 2554547108585472000 |
| 22 | -51090942171709440000 |
| 23 | -1175091669949317120000 |