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 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 136 |
| 5 | 941 |
| 6 | 6864 |
| 7 | 52006 |
| 8 | 405312 |
| 9 | 3228654 |
| 10 | 26170764 |
| 11 | 215166638 |
| 12 | 1789998808 |
| 13 | 15040070843 |
| 14 | 127450104568 |
| 15 | 1087988783356 |
| 16 | 9347556057040 |
| 17 | 80766068931498 |
| 18 | 701359680126592 |
| 19 | 6117887649100980 |
| 20 | 53581405635501276 |
| 21 | 470988258063461393 |