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 | 0 |
| 2 | 0 |
| 3 | -6 |
| 4 | -24 |
| 5 | -120 |
| 6 | -360 |
| 7 | 0 |
| 8 | 20160 |
| 9 | 302400 |
| 10 | 3628800 |
| 11 | 39916800 |
| 12 | 419126400 |
| 13 | 4151347200 |
| 14 | 36324288000 |
| 15 | 207048441600 |
| 16 | -1743565824000 |
| 17 | -103742166528000 |
| 18 | -2925529096089600 |
| 19 | -69945932735078400 |
| 20 | -1571249213614080000 |
| 21 | -34354603773794304000 |
| 22 | -741528257908838400000 |