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 | 6 |
| 2 | 30 |
| 3 | 138 |
| 4 | 694 |
| 5 | 3526 |
| 6 | 18012 |
| 7 | 92140 |
| 8 | 471566 |
| 9 | 2413794 |
| 10 | 12356010 |
| 11 | 63250314 |
| 12 | 323779348 |
| 13 | 1657433992 |
| 14 | 8484446994 |
| 15 | 43432107538 |
| 16 | 222330112286 |
| 17 | 1138113767838 |
| 18 | 5826034724844 |
| 19 | 29823627148788 |
| 20 | 152667942902854 |