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 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 28 |
| 5 | 270 |
| 6 | 3185 |
| 7 | 42830 |
| 8 | 636250 |
| 9 | 10765885 |
| 10 | 227860725 |
| 11 | 6003043950 |
| 12 | 152451368175 |
| 13 | 2205648850800 |
| 14 | 1614364541325 |
| 15 | 6690753945813375 |
| 16 | 787760273195291625 |
| 17 | -6787610390670062625 |
| 18 | -7103289749314032719250 |
| 19 | -59946385622086525694250 |
| 20 | 117473730537013548978420000 |