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 | 21 |
| 2 | 105 |
| 3 | 5460 |
| 4 | 26796 |
| 5 | 1386945 |
| 6 | 6806205 |
| 7 | 352278696 |
| 8 | 1728749400 |
| 9 | 89477401965 |
| 10 | 439095541521 |
| 11 | 22726907820540 |
| 12 | 111528538797060 |
| 13 | 5772545109015321 |
| 14 | 28327809758911845 |
| 15 | 1466203730782071120 |
| 16 | 7195152150224811696 |
| 17 | 372409975073537049285 |
| 18 | 1827540318347343259065 |