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 | 4 |
| 2 | 25 |
| 3 | 150 |
| 4 | 900 |
| 5 | 5400 |
| 6 | 32400 |
| 7 | 194400 |
| 8 | 1166400 |
| 9 | 6998400 |
| 10 | 41990400 |
| 11 | 251942400 |
| 12 | 1511654400 |
| 13 | 9069926400 |
| 14 | 54419558400 |
| 15 | 326517350400 |
| 16 | 1959104102400 |
| 17 | 11754624614400 |
| 18 | 70527747686400 |
| 19 | 423166486118400 |
| 20 | 2538998916710400 |