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 | 4 |
| 4 | 20 |
| 5 | 129 |
| 6 | 1020 |
| 7 | 9542 |
| 8 | 103063 |
| 9 | 1262134 |
| 10 | 17279744 |
| 11 | 261531315 |
| 12 | 4335950346 |
| 13 | 78146040374 |
| 14 | 1521220672933 |
| 15 | 31808447321848 |
| 16 | 711019048106744 |
| 17 | 16919695824732249 |
| 18 | 427046133330613512 |
| 19 | 11394750238551713066 |
| 20 | 320486422239301377007 |
| 21 | 9476411014096567341034 |