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 | -1 |
| 4 | -7 |
| 5 | -3 |
| 6 | 97 |
| 7 | 275 |
| 8 | -2063 |
| 9 | -15015 |
| 10 | 53409 |
| 11 | 968167 |
| 12 | -752343 |
| 13 | -77000363 |
| 14 | -166831871 |
| 15 | 7433044411 |
| 16 | 43685848289 |
| 17 | -843598411471 |
| 18 | -9398558916159 |
| 19 | 107426835190735 |
| 20 | 2116926930779225 |
| 21 | -14072980460605907 |