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) |
|---|---|
| 4 | 1901 |
| 5 | 19001 |
| 6 | 198901 |
| 7 | 1909081 |
| 8 | 19986091 |
| 9 | 199800091 |
| 10 | 1999880101 |
| 11 | 19999919011 |
| 12 | 199999069901 |
| 13 | 1999998661891 |
| 14 | 19999999196861 |
| 15 | 199999990066801 |
| 16 | 1999999999899101 |
| 17 | 19999999999898161 |
| 18 | 199999999998806191 |
| 19 | 1999999999999988911 |
| 20 | 19999999999998191191 |
| 21 | 199999999999986661691 |