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 | 5 |
| 2 | 18 |
| 3 | 78 |
| 4 | 408 |
| 5 | 2520 |
| 6 | 18000 |
| 7 | 146160 |
| 8 | 1330560 |
| 9 | 13426560 |
| 10 | 148780800 |
| 11 | 1796256000 |
| 12 | 23471078400 |
| 13 | 330032102400 |
| 14 | 4969162598400 |
| 15 | 79768136448000 |
| 16 | 1359981342720000 |
| 17 | 24542432538624000 |
| 18 | 467373280518144000 |
| 19 | 9366672731480064000 |