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 | 2 |
| 2 | 6 |
| 3 | 30 |
| 4 | 330 |
| 5 | 4290 |
| 6 | 72930 |
| 7 | 2114970 |
| 8 | 65564070 |
| 9 | 2688126870 |
| 10 | 115589455410 |
| 11 | 5432704404270 |
| 12 | 320529559851930 |
| 13 | 21475480510079310 |
| 14 | 1567710077235789630 |
| 15 | 123849096101627380770 |
| 16 | 10279474976435072603910 |
| 17 | 1038226972619942332994910 |
| 18 | 113166740015573714296445190 |
| 19 | 12787841621759829715498306470 |