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 | 3 |
| 2 | 21 |
| 3 | 171 |
| 4 | 1509 |
| 5 | 13995 |
| 6 | 134277 |
| 7 | 1320651 |
| 8 | 13237221 |
| 9 | 134682219 |
| 10 | 1387100229 |
| 11 | 14430764043 |
| 12 | 151415596197 |
| 13 | 1600364733867 |
| 14 | 17022016484613 |
| 15 | 182055719885643 |
| 16 | 1956671540189541 |
| 17 | 21121180251536619 |
| 18 | 228880429935661509 |
| 19 | 2488986535173458571 |
| 20 | 27152943714786745893 |