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 | 5 |
| 3 | 20 |
| 4 | 94 |
| 5 | 507 |
| 6 | 3009 |
| 7 | 19350 |
| 8 | 132920 |
| 9 | 966962 |
| 10 | 7396366 |
| 11 | 59173897 |
| 12 | 492995320 |
| 13 | 4262193275 |
| 14 | 38125138575 |
| 15 | 351960913470 |
| 16 | 3346157796060 |
| 17 | 32700768584100 |
| 18 | 327957494280000 |
| 19 | 3370522049859990 |
| 20 | 35451669429671520 |
| 21 | 381183654441916290 |