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 | -2 |
| 3 | 1 |
| 4 | -4 |
| 5 | 21 |
| 6 | -196 |
| 7 | 1023 |
| 8 | -5440 |
| 9 | 65145 |
| 10 | -1237456 |
| 11 | 10925883 |
| 12 | -69882880 |
| 13 | 1994183205 |
| 14 | -39099282496 |
| 15 | 372390766023 |
| 16 | -6270496768000 |
| 17 | 158096182329585 |
| 18 | -3268815510804736 |
| 19 | 64115697136312563 |
| 20 | -1009052458754375680 |
| 21 | 27389518837925527965 |
| 22 | -924645800211698308096 |
| 23 | 19391677044464348893503 |