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 | 1 |
| 3 | 6 |
| 4 | 40 |
| 5 | 285 |
| 6 | 2126 |
| 7 | 16380 |
| 8 | 129456 |
| 9 | 1043460 |
| 10 | 8544965 |
| 11 | 70893054 |
| 12 | 594610536 |
| 13 | 5033644070 |
| 14 | 42952562100 |
| 15 | 369061673400 |
| 16 | 3190379997272 |
| 17 | 27727712947836 |
| 18 | 242135589539124 |
| 19 | 2123541227823800 |
| 20 | 18695484623015200 |
| 21 | 165169213716082765 |