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 | 0 |
| 2 | 6 |
| 3 | 12 |
| 4 | 90 |
| 5 | 360 |
| 6 | 2040 |
| 7 | 10080 |
| 8 | 54810 |
| 9 | 290640 |
| 10 | 1588356 |
| 11 | 8676360 |
| 12 | 47977776 |
| 13 | 266378112 |
| 14 | 1488801600 |
| 15 | 8355739392 |
| 16 | 47104393050 |
| 17 | 266482019232 |
| 18 | 1512589408044 |
| 19 | 8610448069080 |
| 20 | 49144928795820 |
| 21 | 281164160225520 |
| 22 | 1612061452900080 |
| 23 | 9261029179733760 |
| 24 | 53299490722049520 |