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) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 10 |
| 6 | 42 |
| 7 | 357 |
| 8 | 2400 |
| 9 | 20142 |
| 10 | 180280 |
| 11 | 1814395 |
| 12 | 19944804 |
| 13 | 239500794 |
| 14 | 3113326062 |
| 15 | 43589143560 |
| 16 | 653834280960 |
| 17 | 10461394943992 |
| 18 | 177843662409312 |
| 19 | 3201186852863991 |
| 20 | 60822549182544440 |
| 21 | 1216451004087794832 |
| 22 | 25545471063559372750 |
| 23 | 562000363888803839989 |