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 | 0 |
| 3 | 18 |
| 4 | 36 |
| 5 | 120 |
| 6 | 4860 |
| 7 | 33264 |
| 8 | 241920 |
| 9 | 5598720 |
| 10 | 72364320 |
| 11 | 879500160 |
| 12 | 18172978560 |
| 13 | 331463508480 |
| 14 | 5726430597888 |
| 15 | 126134466796800 |
| 16 | 2836325702246400 |
| 17 | 62773403361177600 |
| 18 | 1562890149787392000 |
| 19 | 41009994647421972480 |
| 20 | 1090182759179092992000 |