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 | 9 |
| 2 | 67 |
| 3 | 519 |
| 4 | 4111 |
| 5 | 32799 |
| 6 | 262207 |
| 7 | 2097279 |
| 8 | 16777471 |
| 9 | 134218239 |
| 10 | 1073742847 |
| 11 | 8589936639 |
| 12 | 68719480831 |
| 13 | 549755822079 |
| 14 | 4398046527487 |
| 15 | 35184372121599 |
| 16 | 281474976776191 |
| 17 | 2251799813816319 |
| 18 | 18014398509744127 |
| 19 | 144115188076380159 |