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 | -3 |
| 2 | 0 |
| 3 | 6 |
| 4 | 42 |
| 5 | 318 |
| 6 | 2892 |
| 7 | 31944 |
| 8 | 424596 |
| 9 | 6682740 |
| 10 | 122318928 |
| 11 | 2559121128 |
| 12 | 60275236392 |
| 13 | 1577894836248 |
| 14 | 45427570253712 |
| 15 | 1425885338250432 |
| 16 | 48443767097018256 |
| 17 | 1770703320887526096 |
| 18 | 69273368628184075392 |
| 19 | 2887794188011931364576 |
| 20 | 127778992241790634125984 |