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 | 1 |
| 2 | 9 |
| 3 | 19 |
| 4 | 305 |
| 5 | 156 |
| 6 | 13233 |
| 7 | -23988 |
| 8 | 688113 |
| 9 | -2863070 |
| 10 | 41085704 |
| 11 | -246536784 |
| 12 | 2696513885 |
| 13 | -19410931916 |
| 14 | 187672944300 |
| 15 | -1481383572516 |
| 16 | 13522625165601 |
| 17 | -111877103550195 |
| 18 | 994511499413664 |
| 19 | -8430550720540365 |
| 20 | 74061353032540020 |
| 21 | -636000265949289978 |