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 | 0 |
| 3 | 3 |
| 4 | 16 |
| 5 | 115 |
| 6 | 660 |
| 7 | 5033 |
| 8 | 39936 |
| 9 | 362718 |
| 10 | 3624920 |
| 11 | 39916789 |
| 12 | 478953648 |
| 13 | 6227020787 |
| 14 | 87177645996 |
| 15 | 1307674338105 |
| 16 | 20922779566080 |
| 17 | 355687428095983 |
| 18 | 6402373519409856 |
| 19 | 121645100408831981 |
| 20 | 2432902004460734000 |
| 21 | 51090942171698415483 |
| 22 | 1124000727695858073380 |