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 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 31 |
| 6 | 111 |
| 7 | 454 |
| 8 | 1982 |
| 9 | 9130 |
| 10 | 43547 |
| 11 | 211658 |
| 12 | 1041316 |
| 13 | 5156641 |
| 14 | 25640000 |
| 15 | 127773440 |
| 16 | 637622320 |
| 17 | 3184387573 |
| 18 | 15910938734 |
| 19 | 79521737938 |
| 20 | 397510683092 |
| 21 | 1987259549544 |
| 22 | 9935420434636 |
| 23 | 49674470817194 |