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 | 2 |
| 1 | 20 |
| 2 | 168 |
| 3 | 1320 |
| 4 | 10010 |
| 5 | 74256 |
| 6 | 542640 |
| 7 | 3922512 |
| 8 | 28120950 |
| 9 | 200300100 |
| 10 | 1419269280 |
| 11 | 10013421600 |
| 12 | 70394353848 |
| 13 | 493362138080 |
| 14 | 3448674255840 |
| 15 | 24051721745568 |
| 16 | 167405449649550 |
| 17 | 1163116182943260 |
| 18 | 8068463611408200 |
| 19 | 55891260077406600 |