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 | 1 |
| 3 | -3 |
| 4 | -15 |
| 5 | -23 |
| 6 | 177 |
| 7 | 1253 |
| 8 | 1057 |
| 9 | -37103 |
| 10 | -245471 |
| 11 | 371085 |
| 12 | 15691665 |
| 13 | 76436089 |
| 14 | -608056239 |
| 15 | -10302629131 |
| 16 | -20287425215 |
| 17 | 856245051169 |
| 18 | 8821231566145 |
| 19 | -29959421725155 |
| 20 | -1376333505095631 |
| 21 | -7591883371988471 |
| 22 | 139148719952772849 |