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 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 40 |
| 6 | 190 |
| 7 | 610 |
| 8 | 1660 |
| 9 | 13420 |
| 10 | 174700 |
| 11 | 1326700 |
| 12 | 30818800 |
| 13 | 342140800 |
| 14 | 2534931400 |
| 15 | 16519411000 |
| 16 | 143752426000 |
| 17 | 4842417082000 |
| 18 | 73620307162000 |
| 19 | 687934401562000 |
| 20 | 17165461784680000 |
| 21 | 308493094924720000 |
| 22 | 4585953613991980000 |
| 23 | 53843602355379220000 |