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 | 4 |
| 2 | 30 |
| 3 | 264 |
| 4 | 2490 |
| 5 | 24396 |
| 6 | 244790 |
| 7 | 2496528 |
| 8 | 25763058 |
| 9 | 268243860 |
| 10 | 2812481870 |
| 11 | 29653804824 |
| 12 | 314097641130 |
| 13 | 3339741725404 |
| 14 | 35626286189670 |
| 15 | 381098437754912 |
| 16 | 4086504567333858 |
| 17 | 43912100376527652 |
| 18 | 472743964145437310 |
| 19 | 5097853987059017000 |
| 20 | 55054474579787825562 |