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 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 82 |
| 5 | 397 |
| 6 | 2186 |
| 7 | 13241 |
| 8 | 86578 |
| 9 | 603249 |
| 10 | 4440800 |
| 11 | 34313272 |
| 12 | 276904847 |
| 13 | 2324369733 |
| 14 | 20227700385 |
| 15 | 181987602305 |
| 16 | 1688734327673 |
| 17 | 16129293322211 |
| 18 | 158281104406067 |
| 19 | 1593383284029479 |
| 20 | 16431757177327175 |
| 21 | 173372313294822983 |