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 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 21 |
| 5 | 121 |
| 6 | 715 |
| 7 | 5041 |
| 8 | 40293 |
| 9 | 362887 |
| 10 | 3628681 |
| 11 | 39916801 |
| 12 | 479000895 |
| 13 | 6227020801 |
| 14 | 87178286161 |
| 15 | 1307674368127 |
| 16 | 20922789847653 |
| 17 | 355687428096001 |
| 18 | 6402373705365835 |
| 19 | 121645100408832001 |
| 20 | 2432902008173011101 |
| 21 | 51090942171709445047 |
| 22 | 1124000727777567763201 |