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 | 4 |
| 4 | 19 |
| 5 | 137 |
| 6 | 1356 |
| 7 | 17167 |
| 8 | 264664 |
| 9 | 4803129 |
| 10 | 100181440 |
| 11 | 2359762091 |
| 12 | 61937322624 |
| 13 | 1792399894837 |
| 14 | 56697025885696 |
| 15 | 1946238657504975 |
| 16 | 72058247875111936 |
| 17 | 2862433512904759793 |
| 18 | 121439708940308299776 |
| 19 | 5480390058971655049939 |
| 20 | 262144060822550204416000 |