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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 2 |
| 4 | -6 |
| 5 | 20 |
| 6 | -70 |
| 7 | 256 |
| 8 | -970 |
| 9 | 3772 |
| 10 | -14960 |
| 11 | 60280 |
| 12 | -246090 |
| 13 | 1015700 |
| 14 | -4231216 |
| 15 | 17767456 |
| 16 | -75126078 |
| 17 | 319588340 |
| 18 | -1366846548 |
| 19 | 5873832384 |
| 20 | -25350152100 |
| 21 | 109828012448 |
| 22 | -477486940848 |
| 23 | 2082520454864 |
| 24 | -9109146150050 |
| 25 | 39950535931956 |