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 | 4 |
| 3 | 42 |
| 4 | 420 |
| 5 | 5779 |
| 6 | 83104 |
| 7 | 1306684 |
| 8 | 21283504 |
| 9 | 356648125 |
| 10 | 6100611232 |
| 11 | 105634585546 |
| 12 | 1845124077000 |
| 13 | 32368064972555 |
| 14 | 568794055227200 |
| 15 | 9991239094888864 |
| 16 | 175142529040285920 |
| 17 | 3060545399532144497 |
| 18 | 53279047286232892928 |
| 19 | 923884653765128839312 |
| 20 | 15965368274611453269820 |