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 | 2 |
| 3 | 7 |
| 4 | 32 |
| 5 | 180 |
| 6 | 1210 |
| 7 | 9450 |
| 8 | 84000 |
| 9 | 836920 |
| 10 | 9234400 |
| 11 | 111742400 |
| 12 | 1471023400 |
| 13 | 20925905000 |
| 14 | 319830310800 |
| 15 | 5226116295400 |
| 16 | 90906373958400 |
| 17 | 1676967192700800 |
| 18 | 32697692264036800 |
| 19 | 671856896755844800 |
| 20 | 14509136903381120000 |
| 21 | 328520930667097168000 |