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 | 7 |
| 2 | 0 |
| 3 | -217 |
| 4 | 0 |
| 5 | 17143 |
| 6 | 215488 |
| 7 | 1979503 |
| 8 | 16515072 |
| 9 | 133686287 |
| 10 | 1072741824 |
| 11 | 8588163031 |
| 12 | 68716490752 |
| 13 | 549750987079 |
| 14 | 4398038981568 |
| 15 | 35184360698207 |
| 16 | 281474959933440 |
| 17 | 2251799789547679 |
| 18 | 18014398475469760 |
| 19 | 144115188028809991 |