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 | 6 |
| 4 | 51 |
| 5 | 520 |
| 6 | 6665 |
| 7 | 102942 |
| 8 | 1864135 |
| 9 | 38742048 |
| 10 | 909090909 |
| 11 | 23775972550 |
| 12 | 685853880635 |
| 13 | 21633936185160 |
| 14 | 740800455037201 |
| 15 | 27368368148803710 |
| 16 | 1085102592571150095 |
| 17 | 45957792327018709120 |
| 18 | 2070863582910344082917 |
| 19 | 98920982783015679456198 |