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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 3 |
| 5 | 21 |
| 6 | 189 |
| 7 | 2457 |
| 8 | 36855 |
| 9 | 700245 |
| 10 | 17506125 |
| 11 | 472665375 |
| 12 | 15597957375 |
| 13 | 577124422875 |
| 14 | 22507852492125 |
| 15 | 967837657161375 |
| 16 | 47424045200907375 |
| 17 | 2608322486049905625 |
| 18 | 148674381704844620625 |
| 19 | 9366486047405211099375 |
| 20 | 627554565176149143658125 |
| 21 | 43301264997154290912410625 |