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 | 3 |
| 3 | -1 |
| 4 | 41 |
| 5 | 299 |
| 6 | 4531 |
| 7 | 74507 |
| 8 | 1474481 |
| 9 | 33540119 |
| 10 | 864507491 |
| 11 | 24891022199 |
| 12 | 791755864153 |
| 13 | 27571976573699 |
| 14 | 1043247441846611 |
| 15 | 42615848603499779 |
| 16 | 1869129393654945761 |
| 17 | 87605345727468933167 |
| 18 | 4369604246576366377411 |
| 19 | 231091472431638655755119 |