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 | 3 |
| 3 | 20 |
| 4 | 205 |
| 5 | 2604 |
| 6 | 39991 |
| 7 | 720600 |
| 8 | 14913081 |
| 9 | 348678440 |
| 10 | 9090909091 |
| 11 | 261535698060 |
| 12 | 8230246567621 |
| 13 | 281241170407092 |
| 14 | 10371206370520815 |
| 15 | 410525522232055664 |
| 16 | 17361641481138401521 |
| 17 | 781282469559318055056 |
| 18 | 37275544492386193492507 |
| 19 | 1879498672877297909667780 |