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 | 3 |
| 1 | 4 |
| 2 | 14 |
| 3 | 72 |
| 4 | 462 |
| 5 | 3432 |
| 6 | 28314 |
| 7 | 252824 |
| 8 | 2401828 |
| 9 | 23984688 |
| 10 | 249554968 |
| 11 | 2687515040 |
| 12 | 29802622140 |
| 13 | 338931781200 |
| 14 | 3940081956450 |
| 15 | 46695460462200 |
| 16 | 562939717794300 |
| 17 | 6890720756158800 |
| 18 | 85507580292334200 |
| 19 | 1074244300649863200 |
| 20 | 13647785546892580200 |
| 21 | 175166360584464768480 |