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 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | -1 |
| 4 | 1 |
| 5 | -1 |
| 6 | -2 |
| 7 | 34 |
| 8 | -324 |
| 9 | 2988 |
| 10 | -28944 |
| 11 | 300816 |
| 12 | -3371040 |
| 13 | 40710240 |
| 14 | -528439680 |
| 15 | 7348717440 |
| 16 | -109109064960 |
| 17 | 1723814265600 |
| 18 | -28888702617600 |
| 19 | 512030734387200 |
| 20 | -9572240647065600 |
| 21 | 188274945999974400 |
| 22 | -3887144020408320000 |
| 23 | 84062926436751360000 |
| 24 | -1900475323780239360000 |