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 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 102 |
| 5 | 870 |
| 6 | 8910 |
| 7 | 106470 |
| 8 | 1454040 |
| 9 | 22339800 |
| 10 | 381364200 |
| 11 | 7161323400 |
| 12 | 146701724400 |
| 13 | 3255661609200 |
| 14 | 77808668137200 |
| 15 | 1992415575150000 |
| 16 | 54420258228336000 |
| 17 | 1579320261543024000 |
| 18 | 48529229906613456000 |
| 19 | 1574046971727454224000 |
| 20 | 53741325186841612320000 |