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 | 4 |
| 3 | 24 |
| 4 | 180 |
| 5 | 1620 |
| 6 | 17040 |
| 7 | 204960 |
| 8 | 2770320 |
| 9 | 41504400 |
| 10 | 681791040 |
| 11 | 12173293440 |
| 12 | 234555773760 |
| 13 | 4847900016960 |
| 14 | 106932303878400 |
| 15 | 2506094618227200 |
| 16 | 62165827044921600 |
| 17 | 1626693694039814400 |
| 18 | 44767280999939097600 |
| 19 | 1292282276155782912000 |