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 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 3 |
| 6 | 9 |
| 7 | 17 |
| 8 | 108 |
| 9 | 324 |
| 10 | 1409 |
| 11 | 3807 |
| 12 | 13365 |
| 13 | 105764 |
| 14 | 347976 |
| 15 | 1825416 |
| 16 | 11309203 |
| 17 | 76330674 |
| 18 | 453496320 |
| 19 | 2638063039 |
| 20 | 19573857765 |
| 21 | 121970492469 |
| 22 | 939636604957 |
| 23 | 5944482289926 |
| 24 | 41069772211068 |
| 25 | 388012765239587 |
| 26 | 2642662404898875 |
| 27 | 21056674779654003 |