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 | 4 |
| 4 | 33 |
| 5 | 300 |
| 6 | 3412 |
| 7 | 40770 |
| 8 | 518043 |
| 9 | 6830545 |
| 10 | 92909684 |
| 11 | 1295151600 |
| 12 | 18426823044 |
| 13 | 266696759064 |
| 14 | 3916798516462 |
| 15 | 58253090490630 |
| 16 | 875948658280305 |
| 17 | 13299481192954961 |
| 18 | 203661940884670135 |
| 19 | 3142707632566279222 |
| 20 | 48829032430870168660 |
| 21 | 763383551090733489744 |