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 | 12 |
| 3 | 56 |
| 4 | 294 |
| 5 | 1722 |
| 6 | 11256 |
| 7 | 82224 |
| 8 | 670662 |
| 9 | 6084578 |
| 10 | 61030536 |
| 11 | 672041328 |
| 12 | 8067200092 |
| 13 | 104884001796 |
| 14 | 1468416141744 |
| 15 | 22026397243680 |
| 16 | 352422956979270 |
| 17 | 5991192602253810 |
| 18 | 107841475915703880 |
| 19 | 2048988077743637520 |
| 20 | 40979761692719279220 |
| 21 | 860574996085362738060 |