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 | 4 |
| 2 | 23 |
| 3 | 117 |
| 4 | 609 |
| 5 | 3159 |
| 6 | 16389 |
| 7 | 85041 |
| 8 | 441225 |
| 9 | 2289339 |
| 10 | 11878281 |
| 11 | 61631001 |
| 12 | 319774761 |
| 13 | 1659164103 |
| 14 | 8608637997 |
| 15 | 44666257401 |
| 16 | 231752633913 |
| 17 | 1202457662523 |
| 18 | 6238998904833 |
| 19 | 32371291359585 |
| 20 | 167959719216009 |
| 21 | 871465613342823 |