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 | 2 |
| 3 | 4 |
| 4 | 18 |
| 5 | 126 |
| 6 | 1301 |
| 7 | 16808 |
| 8 | 262162 |
| 9 | 4782973 |
| 10 | 100000127 |
| 11 | 2357947692 |
| 12 | 61917365541 |
| 13 | 1792160394038 |
| 14 | 56693912392105 |
| 15 | 1946195068359504 |
| 16 | 72057594038190098 |
| 17 | 2862423051509815794 |
| 18 | 121439531096599036046 |
| 19 | 5480386857784802185940 |
| 20 | 262144000000000100000143 |