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 | 6 |
| 3 | 72 |
| 4 | 576 |
| 5 | 3840 |
| 6 | 23040 |
| 7 | 129024 |
| 8 | 688128 |
| 9 | 3538944 |
| 10 | 17694720 |
| 11 | 86507520 |
| 12 | 415236096 |
| 13 | 1962934272 |
| 14 | 9160359936 |
| 15 | 42278584320 |
| 16 | 193273528320 |
| 17 | 876173328384 |
| 18 | 3942779977728 |
| 19 | 17626545782784 |
| 20 | 78340203479040 |
| 21 | 346346162749440 |