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 | 4 |
| 4 | -5 |
| 5 | 17 |
| 6 | -40 |
| 7 | 144 |
| 8 | -459 |
| 9 | 1517 |
| 10 | -5111 |
| 11 | 17747 |
| 12 | -62074 |
| 13 | 219292 |
| 14 | -782602 |
| 15 | 2816664 |
| 16 | -10205754 |
| 17 | 37203230 |
| 18 | -136360106 |
| 19 | 502219652 |
| 20 | -1857659296 |
| 21 | 6897983144 |
| 22 | -25704335380 |
| 23 | 96090440940 |
| 24 | -360265425619 |
| 25 | 1354343161419 |
| 26 | -5103948546609 |
| 27 | 19278502980063 |
| 28 | -72972099256954 |