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 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 12 |
| 5 | 64 |
| 6 | 470 |
| 7 | 3828 |
| 8 | 36456 |
| 9 | 387840 |
| 10 | 4603392 |
| 11 | 60061440 |
| 12 | 855664656 |
| 13 | 13207470912 |
| 14 | 219609303888 |
| 15 | 3912940891104 |
| 16 | 74377769483520 |
| 17 | 1502277409668096 |
| 18 | 32130095812624512 |
| 19 | 725400731911792896 |
| 20 | 17240044059713320704 |
| 21 | 430231117562438446080 |
| 22 | 11248105572520779755520 |