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 | 4 |
| 3 | 12 |
| 4 | 54 |
| 5 | 312 |
| 6 | 2136 |
| 7 | 16800 |
| 8 | 149160 |
| 9 | 1475280 |
| 10 | 16081920 |
| 11 | 191530080 |
| 12 | 2473999920 |
| 13 | 34446303360 |
| 14 | 514240110720 |
| 15 | 8193624284160 |
| 16 | 138780284791680 |
| 17 | 2489891543596800 |
| 18 | 47169750454848000 |
| 19 | 940914453958617600 |
| 20 | 19712190644360121600 |