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 | 7 |
| 2 | 14 |
| 3 | 70 |
| 4 | 126 |
| 5 | 574 |
| 6 | 1022 |
| 7 | 4606 |
| 8 | 8190 |
| 9 | 36862 |
| 10 | 65534 |
| 11 | 294910 |
| 12 | 524286 |
| 13 | 2359294 |
| 14 | 4194302 |
| 15 | 18874366 |
| 16 | 33554430 |
| 17 | 150994942 |
| 18 | 268435454 |
| 19 | 1207959550 |
| 20 | 2147483646 |
| 21 | 9663676414 |
| 22 | 17179869182 |
| 23 | 77309411326 |
| 24 | 137438953470 |
| 25 | 618475290622 |
| 26 | 1099511627774 |
| 27 | 4947802324990 |