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 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 3 |
| 6 | 11 |
| 7 | 47 |
| 8 | 253 |
| 9 | 1651 |
| 10 | 12610 |
| 11 | 109744 |
| 12 | 1069355 |
| 13 | 11520785 |
| 14 | 135906642 |
| 15 | 1741702304 |
| 16 | 24089599321 |
| 17 | 357592702647 |
| 18 | 5669840845462 |
| 19 | 95623921546478 |
| 20 | 1709172658222253 |
| 21 | 32271612381443479 |
| 22 | 641820925099092985 |
| 23 | 13410242452064469153 |
| 24 | 293676423537521878381 |