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 | -5 |
| 4 | -23 |
| 5 | -59 |
| 6 | 1321 |
| 7 | 9871 |
| 8 | 39985 |
| 9 | -1512503 |
| 10 | -16027919 |
| 11 | -89148509 |
| 12 | 4751428441 |
| 13 | 65256458125 |
| 14 | 461686022617 |
| 15 | -31737431328329 |
| 16 | -535583971806239 |
| 17 | -4599769739165039 |
| 18 | 387180506424212065 |
| 19 | 7750866424109754187 |
| 20 | 78298694889496869961 |
| 21 | -7798395141074580424619 |