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 | 0 |
| 2 | 6 |
| 3 | 20 |
| 4 | 180 |
| 5 | 644 |
| 6 | 5502 |
| 7 | 20292 |
| 8 | 174456 |
| 9 | 654632 |
| 10 | 5673140 |
| 11 | 21528000 |
| 12 | 187675644 |
| 13 | 717800628 |
| 14 | 6284986554 |
| 15 | 24178479500 |
| 16 | 212408191568 |
| 17 | 820811282352 |
| 18 | 7229648901024 |
| 19 | 28037230854096 |
| 20 | 247468885359240 |
| 21 | 962488105227160 |
| 22 | 8510025522045036 |
| 23 | 33177800527098040 |
| 24 | 293772371437293720 |