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 | 7 |
| 4 | 55 |
| 5 | 840 |
| 6 | 15189 |
| 7 | 309607 |
| 8 | 6671842 |
| 9 | 149850849 |
| 10 | 3471296793 |
| 11 | 82442359291 |
| 12 | 1998559329142 |
| 13 | 49290785442796 |
| 14 | 1233639304644946 |
| 15 | 31268489727956101 |
| 16 | 801335133177932829 |
| 17 | 20736286803363051714 |
| 18 | 541224489038545084067 |
| 19 | 14234799536039481373552 |
| 20 | 376974819516101224941091 |