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 | 0 |
| 1 | 1 |
| 2 | 7 |
| 3 | 48 |
| 4 | 327 |
| 5 | 2221 |
| 6 | 15060 |
| 7 | 102012 |
| 8 | 690519 |
| 9 | 4671819 |
| 10 | 31596447 |
| 11 | 213633696 |
| 12 | 1444131108 |
| 13 | 9760401756 |
| 14 | 65957919496 |
| 15 | 445671648228 |
| 16 | 3011064814455 |
| 17 | 20341769686311 |
| 18 | 137412453018933 |
| 19 | 928188965638464 |
| 20 | 6269358748632207 |
| 21 | 42343731580741821 |