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 | 4 |
| 3 | 15 |
| 4 | 73 |
| 5 | 390 |
| 6 | 2641 |
| 7 | 19208 |
| 8 | 164585 |
| 9 | 1541746 |
| 10 | 16158341 |
| 11 | 181370552 |
| 12 | 2283224065 |
| 13 | 30160914446 |
| 14 | 434715492485 |
| 15 | 6655132252876 |
| 16 | 109315669969217 |
| 17 | 1879289179364690 |
| 18 | 34719396682318021 |
| 19 | 666070910669770400 |
| 20 | 13590051478686198401 |
| 21 | 289043813095242038422 |