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 | 4 |
| 5 | 34 |
| 6 | 274 |
| 7 | 2312 |
| 8 | 21034 |
| 9 | 207790 |
| 10 | 2228892 |
| 11 | 25890642 |
| 12 | 324477994 |
| 13 | 4370180744 |
| 14 | 63007469346 |
| 15 | 968847653702 |
| 16 | 15834053988732 |
| 17 | 274170226919434 |
| 18 | 5015004366420178 |
| 19 | 96645631069563928 |
| 20 | 1957433140982004026 |