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) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 110 |
| 5 | 640 |
| 6 | 3870 |
| 7 | 24084 |
| 8 | 153306 |
| 9 | 993978 |
| 10 | 6544242 |
| 11 | 43652340 |
| 12 | 294469974 |
| 13 | 2006018748 |
| 14 | 13784115468 |
| 15 | 95444016984 |
| 16 | 665407010349 |
| 17 | 4667570034444 |
| 18 | 32922870719664 |
| 19 | 233389493503968 |
| 20 | 1662048903052380 |
| 21 | 11885333877149532 |