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 | 30 |
| 3 | 224 |
| 4 | 1680 |
| 5 | 12672 |
| 6 | 96096 |
| 7 | 732160 |
| 8 | 5601024 |
| 9 | 42997760 |
| 10 | 331082752 |
| 11 | 2556051456 |
| 12 | 19778969600 |
| 13 | 153363087360 |
| 14 | 1191302553600 |
| 15 | 9268801044480 |
| 16 | 72219408138240 |
| 17 | 563445537177600 |
| 18 | 4401135695953920 |
| 19 | 34414895667609600 |
| 20 | 269374774271016960 |
| 21 | 2110381254330286080 |