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 | 2 |
| 2 | 9 |
| 3 | 52 |
| 4 | 336 |
| 5 | 2304 |
| 6 | 16368 |
| 7 | 118976 |
| 8 | 878592 |
| 9 | 6562816 |
| 10 | 49447424 |
| 11 | 375072768 |
| 12 | 2860343296 |
| 13 | 21909012480 |
| 14 | 168425533440 |
| 15 | 1298753372160 |
| 16 | 10041201131520 |
| 17 | 77809145610240 |
| 18 | 604138825973760 |
| 19 | 4698956908462080 |
| 20 | 36604934482821120 |