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 | 63 |
| 5 | 204 |
| 6 | 682 |
| 7 | 2340 |
| 8 | 381300 |
| 9 | 1398101 |
| 10 | 5162220 |
| 11 | 71582788 |
| 12 | 1010580540 |
| 13 | 14467258260 |
| 14 | 3059510616420 |
| 15 | 2573485501354569 |
| 16 | 9938978487990060 |
| 17 | 148764065110560900 |
| 18 | 510526106256177860940 |
| 19 | 117943982401427236556700 |
| 20 | 1799331452449680632120820 |