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 | -6 |
| 4 | -23 |
| 5 | -60 |
| 6 | -1 |
| 7 | 1526 |
| 8 | 15121 |
| 9 | 106344 |
| 10 | 579359 |
| 11 | 1870418 |
| 12 | -8716487 |
| 13 | -251210388 |
| 14 | -3217413473 |
| 15 | -31518844530 |
| 16 | -245728084447 |
| 17 | -1260370850736 |
| 18 | 3075924210623 |
| 19 | 208464730479658 |
| 20 | 3846319817704841 |
| 21 | 52691292058337940 |