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 | -510 |
| 3 | -19677 |
| 4 | -262120 |
| 5 | -1953005 |
| 6 | -10076976 |
| 7 | -40348567 |
| 8 | -134177408 |
| 9 | -387057609 |
| 10 | -996371200 |
| 11 | -2318030891 |
| 12 | -4680778752 |
| 13 | -4377478573 |
| 14 | 66517244416 |
| 15 | 1269231008625 |
| 16 | 20854070411264 |
| 17 | 355568840219503 |
| 18 | 6402175346437632 |
| 19 | 121644777721134221 |
| 20 | 2432901496176640000 |
| 21 | 51090941377429393419 |