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 | 3 |
| 2 | 0 |
| 3 | -17 |
| 4 | 0 |
| 5 | 399 |
| 6 | 2800 |
| 7 | 13983 |
| 8 | 61440 |
| 9 | 255583 |
| 10 | 1038576 |
| 11 | 4179663 |
| 12 | 16756480 |
| 13 | 67080303 |
| 14 | 268397040 |
| 15 | 1073691199 |
| 16 | 4294901760 |
| 17 | 17179785663 |
| 18 | 68719371760 |
| 19 | 274877776623 |
| 20 | 1099511467776 |
| 21 | 4398046316623 |
| 22 | 17592185810160 |
| 23 | 70368743897823 |
| 24 | 281474976378880 |
| 25 | 1125899906451999 |