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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 19 |
| 5 | 132 |
| 6 | 991 |
| 7 | 7740 |
| 8 | 62020 |
| 9 | 505857 |
| 10 | 4180132 |
| 11 | 34889514 |
| 12 | 293518072 |
| 13 | 2485191753 |
| 14 | 21153817090 |
| 15 | 180865139538 |
| 16 | 1552289627872 |
| 17 | 13366436688402 |
| 18 | 115425148203235 |
| 19 | 999256943147094 |
| 20 | 8670047414816233 |
| 21 | 75375298322580081 |
| 22 | 656465004512563546 |