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 | -1 |
| 3 | 2 |
| 4 | 11 |
| 5 | -50 |
| 6 | -225 |
| 7 | 1624 |
| 8 | 6769 |
| 9 | -67284 |
| 10 | -269325 |
| 11 | 3416930 |
| 12 | 13339535 |
| 13 | -206070150 |
| 14 | -790943153 |
| 15 | 14409322928 |
| 16 | 54631129553 |
| 17 | -1146901283528 |
| 18 | -4308105301929 |
| 19 | 102417740732658 |
| 20 | 381922055502195 |
| 21 | -10142299865511450 |