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 | 30 |
| 4 | 245 |
| 5 | 2256 |
| 6 | 21849 |
| 7 | 220655 |
| 8 | 2294241 |
| 9 | 24402721 |
| 10 | 264251525 |
| 11 | 2903503779 |
| 12 | 32289673568 |
| 13 | 362755014742 |
| 14 | 4110792367801 |
| 15 | 46933876797456 |
| 16 | 539362815736466 |
| 17 | 6234031681945681 |
| 18 | 72421584940086375 |
| 19 | 845164178044504188 |
| 20 | 9903469546224045896 |
| 21 | 116475680442085941037 |