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 | 2 |
| 3 | 6 |
| 4 | 36 |
| 5 | 240 |
| 6 | 2280 |
| 7 | 27720 |
| 8 | 425040 |
| 9 | 7862400 |
| 10 | 171188640 |
| 11 | 4319330400 |
| 12 | 125199708480 |
| 13 | 4142318019840 |
| 14 | 155388782989440 |
| 15 | 6557345831836800 |
| 16 | 308677784640825600 |
| 17 | 16079233115648102400 |
| 18 | 920518264903690252800 |
| 19 | 57603377545940850624000 |