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 | 6 |
| 4 | 13 |
| 5 | 180 |
| 6 | 501 |
| 7 | 13720 |
| 8 | 34777 |
| 9 | 2014992 |
| 10 | 2512585 |
| 11 | 491642976 |
| 12 | -564313947 |
| 13 | 181714012480 |
| 14 | -836832558275 |
| 15 | 95473740036480 |
| 16 | -856984734161999 |
| 17 | 68029327826567424 |
| 18 | -954950936641491951 |
| 19 | 63368301861354866176 |
| 20 | -1238053892876418633155 |
| 21 | 74904417332353810338816 |