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 | 1 |
| 3 | 4 |
| 4 | 15 |
| 5 | 96 |
| 6 | 455 |
| 7 | 4320 |
| 8 | 29295 |
| 9 | 300160 |
| 10 | 2663199 |
| 11 | 36288000 |
| 12 | 348523175 |
| 13 | 5748019200 |
| 14 | 68027248575 |
| 15 | 1116542242816 |
| 16 | 16813959537375 |
| 17 | 334764638208000 |
| 18 | 4954072089341375 |
| 19 | 115242726703104000 |
| 20 | 1966765155600364119 |
| 21 | 45415699475660800000 |
| 22 | 930312555383281809375 |