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 | -126 |
| 3 | -2181 |
| 4 | -16360 |
| 5 | -78005 |
| 6 | -279216 |
| 7 | -818503 |
| 8 | -2056832 |
| 9 | -4420089 |
| 10 | -6371200 |
| 11 | 20429629 |
| 12 | 443169792 |
| 13 | 6164272283 |
| 14 | 87072877696 |
| 15 | 1307503508625 |
| 16 | 20922521452544 |
| 17 | 355687017757327 |
| 18 | 6402373093507968 |
| 19 | 121645099514960261 |
| 20 | 2432902006896640000 |