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 | 3 |
| 2 | 12 |
| 3 | 54 |
| 4 | 270 |
| 5 | 1458 |
| 6 | 8424 |
| 7 | 51516 |
| 8 | 331452 |
| 9 | 2230740 |
| 10 | 15641424 |
| 11 | 113846472 |
| 12 | 857706408 |
| 13 | 6671592216 |
| 14 | 53465326560 |
| 15 | 440602852752 |
| 16 | 3727748253456 |
| 17 | 32332181692464 |
| 18 | 287111706003648 |
| 19 | 2607272929404000 |
| 20 | 24187186030419936 |
| 21 | 228997933855499808 |
| 22 | 2210786521482955392 |
| 23 | 21746223198911853504 |