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 | -1 |
| 3 | 1 |
| 4 | 30 |
| 5 | 404 |
| 6 | 5379 |
| 7 | 76021 |
| 8 | 1155805 |
| 9 | 18931873 |
| 10 | 333434490 |
| 11 | 6295452542 |
| 12 | 127007655461 |
| 13 | 2729179670279 |
| 14 | 62275740709651 |
| 15 | 1504740573206497 |
| 16 | 38398859322225738 |
| 17 | 1032354879165190692 |
| 18 | 29174916098556605939 |
| 19 | 864859538577015162053 |
| 20 | 26840211278794388530737 |