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 | 18 |
| 3 | 91 |
| 4 | 512 |
| 5 | 3169 |
| 6 | 21352 |
| 7 | 155257 |
| 8 | 1209680 |
| 9 | 10039825 |
| 10 | 88318136 |
| 11 | 819958033 |
| 12 | 8004898600 |
| 13 | 81913041721 |
| 14 | 876117919616 |
| 15 | 9770201709649 |
| 16 | 113347591376672 |
| 17 | 1365288066794017 |
| 18 | 17043527322085096 |
| 19 | 220145837754233713 |
| 20 | 2937871757773069496 |
| 21 | 40451715334029650953 |