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 | 4 |
| 2 | 16 |
| 3 | 68 |
| 4 | 324 |
| 5 | 1776 |
| 6 | 11208 |
| 7 | 80664 |
| 8 | 654600 |
| 9 | 5926080 |
| 10 | 59283552 |
| 11 | 649972704 |
| 12 | 7754418528 |
| 13 | 100047107520 |
| 14 | 1388392475328 |
| 15 | 20625806330496 |
| 16 | 326648173136256 |
| 17 | 5494182397387776 |
| 18 | 97821610887785472 |
| 19 | 1838137437962182656 |
| 20 | 36354781509406470144 |
| 21 | 754959568444846387200 |