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 | 12 |
| 4 | 63 |
| 5 | 420 |
| 6 | 3345 |
| 7 | 31080 |
| 8 | 330225 |
| 9 | 3946320 |
| 10 | 52401195 |
| 11 | 765404640 |
| 12 | 12196214415 |
| 13 | 210533843520 |
| 14 | 3913845680745 |
| 15 | 77955813936000 |
| 16 | 1656235524168225 |
| 17 | 37387344753158400 |
| 18 | 893615568162592275 |
| 19 | 22545399132243187200 |
| 20 | 598744483093370188575 |
| 21 | 16696076277239091532800 |