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 | 1 |
| 4 | 17 |
| 5 | 109 |
| 6 | 707 |
| 7 | 5023 |
| 8 | 40301 |
| 9 | 362857 |
| 10 | 3628771 |
| 11 | 39916769 |
| 12 | 479001563 |
| 13 | 6227020759 |
| 14 | 87178291157 |
| 15 | 1307674367953 |
| 16 | 20922789887947 |
| 17 | 355687428095941 |
| 18 | 6402373705727939 |
| 19 | 121645100408831933 |
| 20 | 2432902008176639929 |
| 21 | 51090942171709439927 |
| 22 | 1124000727777607679921 |