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 | 144 |
| 4 | 696 |
| 5 | 3330 |
| 6 | 15774 |
| 7 | 74484 |
| 8 | 351192 |
| 9 | 1651806 |
| 10 | 7753182 |
| 11 | 36342882 |
| 12 | 170163366 |
| 13 | 795893904 |
| 14 | 3719252820 |
| 15 | 17367159072 |
| 16 | 81042611532 |
| 17 | 377955686508 |
| 18 | 1761732754584 |