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 | 4 |
| 3 | 6 |
| 4 | 88 |
| 5 | 420 |
| 6 | 5148 |
| 7 | 44520 |
| 8 | 587424 |
| 9 | 7203168 |
| 10 | 109106640 |
| 11 | 1689621120 |
| 12 | 29620245312 |
| 13 | 546547098240 |
| 14 | 10989238893696 |
| 15 | 233884517368320 |
| 16 | 5324618721070080 |
| 17 | 128058198711690240 |
| 18 | 3260308438558826496 |
| 19 | 87336328336058603520 |
| 20 | 2459915920512955929600 |