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 | 12 |
| 4 | 48 |
| 5 | 360 |
| 6 | 2520 |
| 7 | 22680 |
| 8 | 221760 |
| 9 | 2298240 |
| 10 | 28425600 |
| 11 | 385862400 |
| 12 | 5269017600 |
| 13 | 80951270400 |
| 14 | 1347631084800 |
| 15 | 21565729785600 |
| 16 | 413922526617600 |
| 17 | 8409043612569600 |
| 18 | 172028224598630400 |
| 19 | 3765253760710041600 |
| 20 | 84080417596471296000 |
| 21 | 1935910813364656128000 |