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 | 21 |
| 3 | 121 |
| 4 | 621 |
| 5 | 3121 |
| 6 | 15621 |
| 7 | 78121 |
| 8 | 390621 |
| 9 | 1953121 |
| 10 | 9765621 |
| 11 | 48828121 |
| 12 | 244140621 |
| 13 | 1220703121 |
| 14 | 6103515621 |
| 15 | 30517578121 |
| 16 | 152587890621 |
| 17 | 762939453121 |
| 18 | 3814697265621 |
| 19 | 19073486328121 |
| 20 | 95367431640621 |
| 21 | 476837158203121 |