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 | 3 |
| 2 | 15 |
| 3 | 85 |
| 4 | 519 |
| 5 | 3330 |
| 6 | 22135 |
| 7 | 151089 |
| 8 | 1052805 |
| 9 | 7458236 |
| 10 | 53554548 |
| 11 | 388913046 |
| 12 | 2851368587 |
| 13 | 21076979445 |
| 14 | 156907929177 |
| 15 | 1175381112901 |
| 16 | 8853057357159 |
| 17 | 67007699270040 |
| 18 | 509390314298820 |
| 19 | 3887605401119964 |
| 20 | 29775366104932044 |