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 | 4 |
| 3 | 20 |
| 4 | 126 |
| 5 | 962 |
| 6 | 8646 |
| 7 | 89546 |
| 8 | 1051350 |
| 9 | 13811642 |
| 10 | 200866326 |
| 11 | 3205348346 |
| 12 | 55704133590 |
| 13 | 1047489675962 |
| 14 | 21195507649686 |
| 15 | 459258707587706 |
| 16 | 10610386574074710 |
| 17 | 260385846630175802 |
| 18 | 6764666952807962646 |