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 | 0 |
| 2 | 1 |
| 3 | 5 |
| 4 | 27 |
| 5 | 129 |
| 6 | 761 |
| 7 | 5137 |
| 8 | 40695 |
| 9 | 363815 |
| 10 | 3632629 |
| 11 | 39927183 |
| 12 | 479047667 |
| 13 | 6227155921 |
| 14 | 87178936305 |
| 15 | 1307676395009 |
| 16 | 20922800209903 |
| 17 | 355687462555407 |
| 18 | 6402373891522541 |
| 19 | 121645101063561055 |
| 20 | 2432902011892531179 |