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) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 51 |
| 5 | 176 |
| 6 | 560 |
| 7 | 1743 |
| 8 | 5271 |
| 9 | 15675 |
| 10 | 45925 |
| 11 | 133056 |
| 12 | 381888 |
| 13 | 1087645 |
| 14 | 3077451 |
| 15 | 8658951 |
| 16 | 24245655 |
| 17 | 67602608 |
| 18 | 187789616 |
| 19 | 519924075 |
| 20 | 1435228575 |
| 21 | 3951341811 |
| 22 | 10852291273 |
| 23 | 29740435200 |
| 24 | 81340229376 |
| 25 | 222058995001 |
| 26 | 605201766675 |
| 27 | 1646862596223 |
| 28 | 4474969884411 |