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 | 0 |
| 3 | 3 |
| 4 | -8 |
| 5 | 10 |
| 6 | 6 |
| 7 | -42 |
| 8 | -160 |
| 9 | 2952 |
| 10 | -27720 |
| 11 | 253440 |
| 12 | -2553528 |
| 13 | 28562664 |
| 14 | -349272000 |
| 15 | 4618376280 |
| 16 | -65615072640 |
| 17 | 996952226880 |
| 18 | -16133983959744 |
| 19 | 277093189849536 |
| 20 | -5033937521116800 |
| 21 | 96451913892983040 |
| 22 | -1943937259314019200 |
| 23 | 41112770486238380160 |