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 | 1 |
| 2 | 15 |
| 3 | 55 |
| 4 | 91 |
| 5 | 595 |
| 6 | 5151 |
| 7 | 5995 |
| 8 | 9591 |
| 9 | 1511191 |
| 10 | 51151555 |
| 11 | 195911115 |
| 12 | 511151999595 |
| 13 | 519191199555 |
| 14 | 555595555515 |
| 15 | 595151955555 |
| 16 | 591915955919511 |
| 17 | 15995115959551911 |
| 18 | 159955559191119511 |
| 19 | 9199995595111955111955555 |
| 20 | 1559111919555519991599911911 |