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 | 4 |
| 5 | 60 |
| 6 | -294 |
| 7 | -2800 |
| 8 | 34504 |
| 9 | 197568 |
| 10 | -6087360 |
| 11 | -9146808 |
| 12 | 1488986808 |
| 13 | -5886157992 |
| 14 | -469973309064 |
| 15 | 5492298353880 |
| 16 | 177826238321856 |
| 17 | -4277426240130048 |
| 18 | -72353540601814464 |
| 19 | 3537861051231290880 |
| 20 | 22847222673714931200 |
| 21 | -3226666120379253611136 |