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 | 18 |
| 4 | 114 |
| 5 | 810 |
| 6 | 7140 |
| 7 | 68880 |
| 8 | 766920 |
| 9 | 9304680 |
| 10 | 125086080 |
| 11 | 1814015280 |
| 12 | 28588356720 |
| 13 | 481128888240 |
| 14 | 8678237087520 |
| 15 | 166041500264640 |
| 16 | 3371031116893440 |
| 17 | 72153115744469760 |
| 18 | 1627441316510929920 |
| 19 | 38500269726897538560 |
| 20 | 954533425718494702080 |