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 | 6 |
| 2 | 15 |
| 3 | 50 |
| 4 | 210 |
| 5 | 882 |
| 6 | 4220 |
| 7 | 20640 |
| 8 | 107100 |
| 9 | 563730 |
| 10 | 3036411 |
| 11 | 16514100 |
| 12 | 90778485 |
| 13 | 502474350 |
| 14 | 2799199380 |
| 15 | 15673672238 |
| 16 | 88162569180 |
| 17 | 497847963690 |
| 18 | 2821127257950 |
| 19 | 16035812864940 |
| 20 | 91404065292036 |