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 | 3 |
| 4 | 18 |
| 5 | 172 |
| 6 | 2313 |
| 7 | 40626 |
| 8 | 887326 |
| 9 | 23282964 |
| 10 | 715540140 |
| 11 | 25259729071 |
| 12 | 1008721104654 |
| 13 | 45008479039824 |
| 14 | 2221170817590696 |
| 15 | 120209722115431950 |
| 16 | 7083266027910364710 |
| 17 | 451620678137942740132 |
| 18 | 30990400538494184551692 |
| 19 | 2277988537997377457967690 |
| 20 | 178626191260072536476398000 |