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 | 3 |
| 3 | 25 |
| 4 | 208 |
| 5 | 1928 |
| 6 | 20328 |
| 7 | 244536 |
| 8 | 3347328 |
| 9 | 51858432 |
| 10 | 902874240 |
| 11 | 17523066240 |
| 12 | 375931514880 |
| 13 | 8842225904640 |
| 14 | 226294152053760 |
| 15 | 6258916573056000 |
| 16 | 185978410684416000 |
| 17 | 5906514709831680000 |
| 18 | 199606607730561024000 |
| 19 | 7150186413112651776000 |
| 20 | 270578540735613960192000 |