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 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 26 |
| 6 | 212 |
| 7 | 2108 |
| 8 | 24720 |
| 9 | 334072 |
| 10 | 5112544 |
| 11 | 87396728 |
| 12 | 1650607040 |
| 13 | 34132685120 |
| 14 | 767025716736 |
| 15 | 18612106195456 |
| 16 | 485013257865472 |
| 17 | 13509071081429888 |
| 18 | 400505695457942528 |
| 19 | 12592502771190979712 |
| 20 | 418524228123134068224 |
| 21 | 14661145374751901317888 |