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 | 0 |
| 1 | 0 |
| 2 | 4 |
| 3 | 24 |
| 4 | 436 |
| 5 | 3888 |
| 6 | 29880 |
| 7 | 264460 |
| 8 | 2353136 |
| 9 | 20400352 |
| 10 | 171215320 |
| 11 | 1430108512 |
| 12 | 11962161392 |
| 13 | 99523393628 |
| 14 | 822501750184 |
| 15 | 6763177931936 |
| 16 | 55433124540308 |
| 17 | 453013557727460 |
| 18 | 3690931980743340 |
| 19 | 29988435689294280 |
| 20 | 243064471330287696 |
| 21 | 1965884816120576180 |