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 | -1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 35 |
| 5 | 221 |
| 6 | 1589 |
| 7 | 12979 |
| 8 | 118663 |
| 9 | 1201465 |
| 10 | 13349609 |
| 11 | 161530271 |
| 12 | 2114578091 |
| 13 | 29780308117 |
| 14 | 448995414685 |
| 15 | 7215997736011 |
| 16 | 123153028027919 |
| 17 | 2224451568754289 |
| 18 | 42395429898611153 |
| 19 | 850263899633257015 |
| 20 | 17900292623858042419 |
| 21 | 394701452356069835341 |