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 | 1 |
| 3 | 4 |
| 4 | 3 |
| 5 | 40 |
| 6 | 15 |
| 7 | 420 |
| 8 | 105 |
| 9 | 5040 |
| 10 | 945 |
| 11 | 69300 |
| 12 | 10395 |
| 13 | 1081080 |
| 14 | 135135 |
| 15 | 18918900 |
| 16 | 2027025 |
| 17 | 367567200 |
| 18 | 34459425 |
| 19 | 7856748900 |
| 20 | 654729075 |
| 21 | 183324141000 |
| 22 | 13749310575 |
| 23 | 4638100767300 |
| 24 | 316234143225 |
| 25 | 126493657290000 |
| 26 | 7905853580625 |
| 27 | 3699939475732500 |
| 28 | 213458046676875 |