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 | 66 |
| 3 | 515 |
| 4 | 4100 |
| 5 | 32773 |
| 6 | 262150 |
| 7 | 2097159 |
| 8 | 16777224 |
| 9 | 134217737 |
| 10 | 1073741834 |
| 11 | 8589934603 |
| 12 | 68719476748 |
| 13 | 549755813901 |
| 14 | 4398046511118 |
| 15 | 35184372088847 |
| 16 | 281474976710672 |
| 17 | 2251799813685265 |
| 18 | 18014398509482002 |
| 19 | 144115188075855891 |
| 20 | 1152921504606846996 |
| 21 | 9223372036854775829 |