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 | 4 |
| 2 | 9 |
| 3 | 49 |
| 4 | 9409 |
| 5 | 44944 |
| 6 | 994009 |
| 7 | 9909904 |
| 8 | 99940009 |
| 9 | 404090404 |
| 10 | 9999400009 |
| 11 | 999994000009 |
| 12 | 4004009004004 |
| 13 | 9449494444009 |
| 14 | 99999940000009 |
| 15 | 9999999400000009 |
| 16 | 40004000900040004 |
| 17 | 999999994000000009 |
| 18 | 99999999940000000009 |
| 19 | 400004000090000400004 |
| 20 | 9999999999400000000009 |