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) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 32 |
| 4 | 228 |
| 5 | 1600 |
| 6 | 11204 |
| 7 | 78432 |
| 8 | 549028 |
| 9 | 3843200 |
| 10 | 26902404 |
| 11 | 188316832 |
| 12 | 1318217828 |
| 13 | 9227524800 |
| 14 | 64592673604 |
| 15 | 452148715232 |
| 16 | 3165041006628 |
| 17 | 22155287046400 |
| 18 | 155087009324804 |
| 19 | 1085609065273632 |
| 20 | 7599263456915428 |
| 21 | 53194844198408000 |
| 22 | 372363909388856004 |
| 23 | 2606547365721992032 |