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) |
|---|---|
| 2 | 1 |
| 3 | 4 |
| 4 | 21 |
| 5 | 138 |
| 6 | 864 |
| 7 | 5526 |
| 8 | 34992 |
| 9 | 221724 |
| 10 | 1399680 |
| 11 | 8818632 |
| 12 | 55427328 |
| 13 | 347684400 |
| 14 | 2176782336 |
| 15 | 13604912928 |
| 16 | 84894511104 |
| 17 | 528958247616 |
| 18 | 3291294892032 |
| 19 | 20453047668864 |
| 20 | 126949945835520 |
| 21 | 787089669219072 |
| 22 | 4874877920083968 |
| 23 | 30163307160752640 |
| 24 | 186464080443211776 |
| 25 | 1151689908801235968 |