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 | 4 |
| 1 | 12 |
| 2 | 50 |
| 3 | 252 |
| 4 | 1394 |
| 5 | 8052 |
| 6 | 47450 |
| 7 | 282252 |
| 8 | 1686434 |
| 9 | 10097892 |
| 10 | 60526250 |
| 11 | 362976252 |
| 12 | 2177317874 |
| 13 | 13062296532 |
| 14 | 78368963450 |
| 15 | 470199366252 |
| 16 | 2821153019714 |
| 17 | 16926788715972 |
| 18 | 101560344351050 |
| 19 | 609360902796252 |
| 20 | 3656161927895954 |
| 21 | 21936961102828212 |