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 | 4 |
| 2 | 16 |
| 3 | 76 |
| 4 | 416 |
| 5 | 2576 |
| 6 | 17840 |
| 7 | 137268 |
| 8 | 1170104 |
| 9 | 11050940 |
| 10 | 115885968 |
| 11 | 1353366864 |
| 12 | 17640817784 |
| 13 | 256630492660 |
| 14 | 4153220868128 |
| 15 | 74315436120300 |
| 16 | 1458541231513152 |
| 17 | 31131651836906752 |
| 18 | 716862465409883040 |
| 19 | 17683184383300077828 |
| 20 | 464519709712796199816 |